Absorbent composites comprising a porous macrostructure of absorbent gelling particles and a substrate

ABSTRACT

An absorbent composite having a porous absorbent macrostructure and a substrate. The porous macrostructure has interconnected absorbent gelling particles that are surface crosslinked with cationic, preferably polymeric, amino-epichlorohydrin adducts. Upon contacting liquids such as water or body exudates (e.g., urine), the porous absorbent macrostructure can swell and imbibe the liquids. The composite is useful in absorbent articles such as diapers, adult incontinence pads, and sanitary napkins are disclosed.

FIELD OF THE INVENTION

This invention relates to an absorbent composite comprising a porous,absorbent macrostructure of interconnected absorbent gelling particlesand a substrate that, upon contacting liquids such as water or bodyexudates (e.g., urine), swells and imbibes such liquids, and is usefulin absorbent articles such as diapers, adult incontinence pads, sanitarynapkins, and the like. This invention particularly relates to anabsorbent composite comprising porous macrostructures of connectedabsorbent particles that are surface crosslinked preferably with acationic, more preferably polymeric, amino-epichlorohydrin adduct.

BACKGROUND OF THE INVENTION

Particulate, absorbent, polymeric compositions are capable of absorbinglarge quantities of liquids such as water and body exudates (e.g.,urine) and are further capable of retaining such absorbed liquids undermoderate pressures. The absorption characteristics of such polymericcompositions make them especially useful for incorporation intoabsorbent articles such as diapers. See, for example, U.S. Pat. No.3,699,103 (Harper et al), issued Jun. 13, 1972, and U.S. Pat. No.3,770,731 (Harmon), issued Jun. 20, 1972, that disclose the use ofparticulate, absorbent, polymeric compositions (often referred to as"hydrogels", "superabsorbents", or "hydrocolloid materials") inabsorbent articles.

Conventional particulate, absorbent, polymeric compositions, however,have the limitation that the particles are not immobilized and are freeto migrate during processing and/or use. Migration of the particles canlead to material handling losses during manufacturing as well asnon-homogeneous incorporation of the particles into structures in whichthe particles are being used. A more significant problem, though, occurswhen these particulate materials migrate during or after swelling inuse. Such mobility leads to high resistance to liquid flow through thematerial due to the lack of stable interparticle capillary or liquidtransport channels. This phenomenon is one form of what is commonlyreferred to as "gel blocking."

One attempt to overcome the performance limitations associated withabsorbent particle mobility during use in absorbent articles isincorporation of the particulate, absorbent, polymeric compositions intotissue laminates, i.e. layered absorbent structures. By encapsulatingthe particles between tissue layers, the overall particle mobilitywithin an absorbent structure is diminished. However, upon liquidcontact, the particles within the laminate are often free to moverelative to each other resulting in the breakdown of any pre-existentinterparticle capillary channels.

Another attempted solution is to immobilize the particulate, absorbent,polymeric compositions by the addition of large quantities of liquidpolyhydroxy compounds that act as an adhesive to hold the particlestogether or to a substrate. See, for example, U.S. Pat. No. 4,410,571(Korpman), issued Oct. 18, 1983. While this approach does limitmigration before and, to some extent, during swelling, the particleseventually become detached from each other in the presence of excessliquid, resulting again in the breakdown of any pre-existing capillarychannels between the particles.

Another attempted solution to overcome the problem of absorbent particlemobility is to produce a superabsorbent film by extrusion of a solutionof a linear absorbent polymer and subsequently crosslinking it. See, forexample. U.S. Pat. No. 4,861,539 (Allen et al), issued Aug. 29, 1989(crosslinked with a polyhydroxy compound such as a glycol or glycerol);and U.S. Pat. No. 4,076,673 (Burkholder), issued Feb. 28, 1978(crosslinked with polyamine-polyamide epichlorohydrin adducts such asKymene®). While these superabsorbent films may absorb significantquantities of liquids, they have limited liquid transport propertiesbecause they are essentially non-porous, i.e. lack internal capillarychannels. Indeed, due to the lack of internal capillary channels, thesesuperabsorbent films are especially prone to gel blocking.

A more recent solution proposed to overcome the problem of absorbentparticle mobility is to form these particles into aggregatemacrostructures, typically as sheets of bonded absorbent particles. SeeU.S. Pat. No. 5.102,597 (Roe et al), issued Apr. 7, 1992. Theseaggregate macrostructures are prepared by initially mixing the absorbentparticles with a solution of a nonionic crosslinking agent, water and ahydrophilic organic solvent such as isopropanol. These nonioniccrosslinking agents include polyhydric alcohols (e.g., glycerol),polyaziridine compounds (e.g., 2,2-bishydroxymethylbutanoltris[3-(1-aziridine) propionate]), haloepoxy compounds (e.g.,epicholorhydrin), polyaldehyde compounds (e.g., glutaraldehyde),polyamine compounds (e.g., ethylene amine), and polyisocyanate compounds(e.g., 2,4-toluene diisocyanate), preferably glycerol. See Column 11,lines 22-54. of Roe et al.

Particulate absorbent polymer compositions of the type used in makingthese aggregate macrostructures usually contain multiple carboxy groupsand are typically derived from polycarboxy compounds such as thepolyacrylates. When using glycerol as the crosslinking agent, thehydroxy groups of the glycerol typically react with the carboxy groupsof the polymers present in the absorbent particles by an esterificationreaction. The crosslinked, ester bond formed by glycerol occurs not onlyat the surface of the absorbent particles, but also inside particles.This is due to the fact that glycerol is a nonionic, relatively smallmolecule that can penetrate inside the absorbent particles. Theresulting internal crosslinking leads to a lower absorbent capacity forthe bonded particles of the aggregate macrostructures.

Moreover, the crosslinking reaction between the hydroxy groups of theglycerol and the carboxy groups of the polymers present in the absorbentparticles is relatively slow. Indeed, the glycerol treated absorbentparticles are typically cured at 200° C. for 50 minutes. This providesrelatively brittle sheets of bonded absorbent particles that are moredifficult to handle, especially in making the ultimately desiredabsorbent structures. Accordingly, these brittle sheets need to betreated with a plasticizer, such as a mixture of water and glycerol, tomake them relatively flexible and thus easier to handle in manufacturingabsorbent structures.

In an attempt to overcome the above described problems, preferredabsorbent macrostructures have been made. Such absorbent macrostructuresare disclosed in co-pending, commonly-assigned U.S. application Ser. No.955,635, to Ebrahim Rezai et al, entitled "Porous, AbsorbentMacrostructures of Bonded Absorbent Particles Surface Crosslinked WithCationic Amino-Epichlorohydrin Adducts", Attorney Docket No. 4731, filedOct. 2, 1992, incorporated herein by reference. This applicationdiscloses aggregate macrostructures of bonded absorbent particles usinga crosslinking agent that: (1) reacts rapidly with the carboxy groups ofthe polymer present in the absorbent particles and primarily at thesurface thereof to minimize absorbency effects; (2) provides improvedabsorbency and mechanical properties for the aggregate macrostructures;(3) provides flexible sheets of such aggregate macrostructures that canbe easily made into absorbent structures used in diapers, adultincontinence pads, sanitary napkins and the like: and (4) does notnecessarily require organic solvents such as isopropanol.

Despite these improvements, there remains a need to further improve theabsorbency, mechanical integrity, flexibility, and utility of suchcrosslinked absorbent aggregate macrostructures, particularly at lowbasis weight (where structures are only a few particle diameters inthickness), where there is a greater tendency for individual bondedparticles to break apart upon handling. Especially after these aggregatemacrostructures become wet, and the gelling particles absorb water andbegin to swell, they are more easily broken apart upon handling or inresponse to movement or external forces.

In addition, these aggregate macrostructures, though they can readilyacquire liquids, have limited ability to distribute the liquid away fromthe point of liquid deposition. Upon addition of water to a portion ofthese aggregate macrostructures, in particular macrostructures in theform of sheets, the absorbent gelling particles in that portion of themacrostructure rapidly absorb the water, causing this portion to swelland expand, causing a phenomenon referred to as "waving".

Consequently, there remains a need for further improvements in suchmacrostructures.

Therefore, one object of the present invention is to provide anabsorbent composite comprising an absorbent macrostructure ofinterconnected absorbent gelling particles which can distribute liquidefficiently and effectively throughout portions of the composite distantfrom the point of liquid deposition, without the use of secondarydistribution means.

Another object of the present invention is to improve the structuralintegrity and strength of such absorbent composites comprising porousabsorbent macrostructures prior to its becoming wet with liquids to beabsorbed.

Another object of the present invention is to improve wet integrity andstrength of such absorbent composites.

Still another object of the present invention is to provide a method formaking such absorbent composites.

Another object of the present invention is to provide absorbentdisposable articles, such as diapers and catamenials pads, which haveimproved liquid distribution properties.

And still another object of the present invention is to provideabsorbent disposable articles such as diapers and catamenials which arevery thin and flexible, and which can acquire, distribute and storeliquids very well.

SUMMARY OF THE INVENTION

Briefly stated, the present invention relates to an absorbent compositecomprising at least one absorbent macrostructure layer comprising amultiplicity of interconnected absorbent gelling particles, saidparticles comprising intermolecular crosslinked absorbent molecules, andat least one substrate bonded to the absorbent macrostructure layer by acrosslinking agent capable of crosslinking the absorbent molecules ofthe absorbent gelling particles.

One aspect of the invention is an absorbent composite comprising (a) afirst absorbent macrostructure layer having a first and a secondsurface, comprising a multiplicity of interconnected absorbent gellingparticles, said particles comprising a plurality of intermolecularcrosslinked absorbent molecules, wherein at least a portion of thesurfaces of the absorbent gelling particles are crosslinked, and (b) afirst substrate having a first surface bonded to the first surface ofthe absorbent macrostructure layer by a crosslinking agent capable ofcrosslinking the absorbent molecules of the absorbent gelling particles.

In another aspect of the invention, an absorbent composite comprises (a)a plurality of absorbent macrostructure layers, each layer having afirst and a second surface and comprising a multiplicity ofinterconnected absorbent gelling particles, said particles comprising aplurality of intermolecular crosslinked absorbent molecules, wherein atleast a portion of the surfaces of the particles are crosslinked, and(b) a plurality of substrates attached, preferably bonded, alternatelyto the plurality of absorbent macrostructure layers by a crosslinkingagent capable of crosslinking the absorbent molecules of the absorbentgelling particles.

In yet another aspect of the invention, an absorbent composite comprises(a) at least one absorbent macrostructure layer comprising amultiplicity of interconnected absorbent gelling particles comprisingintermolecular crosslinked absorbent molecules, wherein at least aportion of the surfaces of the particles are crosslinked, and (b) atleast one supporting means bonded to said absorbent macrostructure layerby a crosslinking agent capable of crosslinking said absorbentmolecules, for supporting the bonding of said multiplicity of absorbentgelling particles.

In still another aspect of the invention, an absorbent compositecomprises (a) at least one absorbent macrostructure layer comprising amultiplicity of interconnected absorbent gelling particles comprisingintermolecular crosslinked absorbent molecules, wherein at least aportion of the surfaces of the particles are crosslinked, and (b) atleast one distributing means bonded to said absorbent macrostructurelayer by a crosslinking agent capable of crosslinking said absorbentmolecules, for distributing liquid to be absorbed to said absorbentmacrostructure layer.

Preferably in the absorbent gelling particles, the crosslinked surfaceportion has a higher level of crosslinking than the remaining portion ofthe particle. Also preferably, the absorbent gelling particles areconnected through the crosslinked surface portions. More preferably, thecrosslinking agent is a cationic amino-epichlorohydrin adduct, mostpreferably Kymene®.

The present invention further relates to an absorbent article. Theabsorbent article comprises: (i) a liquid pervious topsheet; (ii) aliquid impervious backsheet; and (iii) an absorbent assembly positionedbetween the topsheet and the backsheet. The absorbent assembly comprisesat least one absorbent composite described above.

The present invention further relates to a method for making a layeredabsorbent composite from substantially water-insoluble, absorbenthydrogel-forming polymer particles. An amount of a substrate attachingmeans is applied to an area of a first surface of a substrate. Thesubstrate attaching means preferably comprises a crosslinking agent inliquid form which is capable of crosslinking with the polymer of theabsorbent hydrogel-forming particles and bonding with the first surfaceof the substrate. A predetermined amount of the absorbenthydrogel-forming polymer particles is added as a layer to the area, suchthat the particles become at least partially contacted with the amountof the crosslinking agent, thereby forming a layer of the absorbentpolymer particles. The crosslinking agent bonds to the first surface ofthe substrate and crosslinks the contacted surfaces of the particles.The exposed surfaces of the layer of absorbent polymer particles arethen contacted with an additional amount of a crosslinking agent to atleast partially, preferably completely, crosslink the polymer at thesurface of the absorbent polymer particles. Successive additional layersof absorbent gelling particles and crosslinking agent can then beapplied to form an absorbent macrostructure layer of interconnectedsurface-crosslinked absorbent hydrogel-forming particles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a continuous absorbent composite of oneembodiment according to the present invention.

FIGS. 2, 3, 4 and 5 are sectional views of absorbent composites of otherembodiments according to the present invention.

FIGS. 6, 7, 8, 9, 10, 11, and 12 are perspective views of absorbentcomposites of yet other embodiments according to the present invention.

FIG. 13 is a photomicrograph (magnification 34.9×) of a section of aporous, absorbent macrostructure according to the present invention.

FIG. 14 is an enlarged, portion (magnification 75×) of themacrostructure shown in FIG. 13.

FIG. 15 is a further enlarged portion (magnification 200×) of themacrostructure shown in FIG. 14.

FIG. 16 is a further enlarged portion (magnification 400×) of themacrostructure shown in FIG. 15.

FIGS. 17A and 17B are perspective views of absorbent composites of stillother embodiments according to the present invention.

FIG. 18 is a perspective view of a slitted absorbent composite for usein a method of making a non-continuous absorbent composite having anet-like shape according to the present invention.

FIG. 18A shows a portion of a pattern of lines which can be usedalternatively as a pattern of slits in a method of making anon-continuous absorbent composite of the present invention.

FIG. 19 is a simplified perspective view of an apparatus for makingabsorbent macrostructures and absorbent composites of the presentinvention in the form of sheets.

FIG. 20 is a simplified perspective view of an apparatus for forming acontinuous slitted absorbent composite of the present invention.

FIG. 21 is a plan view of a blade plate for forming slits in anabsorbent composite.

FIG. 22 is a cross-sectional view of the blade plate of FIG. 21 throughline 22--22.

FIG. 23 is a simplified perspective view of a recess roll used in amethod for forming slits in an absorbent composite.

FIG. 24 is a partial cross-sectional view of the recess roll of FIG. 23through line 24--24.

FIG. 25 is a partial cross-sectional view of the slit forming device 420shown in FIG. 20 through line 25--25.

FIG. 26 is a perspective view of a disposable diaper embodimentaccording to the present invention wherein portions of the topsheet havebeen cut-away to more clearly show an underlying absorbent core whichcomprises an non-continuous absorbent composite of the presentinvention.

FIG. 27 is a cross-sectional view of the non-continuous absorbentcomposite core of the diaper shown in FIG. 26 taken along sectional line27--27.

FIG. 28 is a perspective view of another disposable diaper embodimentaccording to the present invention wherein portions of the topsheet havebeen cut away to more clearly show an underlying absorbent core whichcomprises an non-continuous absorbent composite of the presentinvention.

DETAILED DESCRIPTION OF ABSORBENT COMPOSITES OF THE INVENTION

A. Structure of an Absorbent Composite

An absorbent composite according to the present invention can comprise acontinuous composite structure wherein the absorbent macrostructurelayer is substantially continuous throughout the plane of the composite.A continuous absorbent composite according to the present inventioncomprises a porous absorbent macrostructure layer and a substrate layerassociated with, preferably attached or bonded to, the macrostructurelayer. One typical example of a continuous absorbent composite structureis shown in FIG. 1.

The absorbent macrostructure layer comprises a multiplicity ofinterconnected absorbent gelling particles. The absorbent gellingparticle are formed from absorbent polymer materials for absorbingliquids such as water and/or body exudates (e.g., urine or menses). Theabsorbent macrostructure layer is capable of acquiring, retaining andabsorbing large quantities of such liquids. In preferred embodiments,the absorbent composite is in the form of a sheet and comprises anabsorbent macrostructure layer and a substrate layer which areco-extensive in the plane of the composite, as shown in FIG. 1.

The absorbent composite can comprise an additional porous absorbentmacrostructure layer, or an additional substrate layer, attached orbonded thereto to form a sandwich structure as shown in FIGS. 2 and 6,respectively. In another embodiment, an continuous absorbent compositecomprises a plurality of substrate layers interposed alternatelybetween, and attached or bonded to, a plurality of porous absorbentmacrostructure layers. Examples of such layered structures are shown inFIGS. 3, 4 and 5.

FIG. 7 shows another embodiment of a continuous absorbent composite 70comprising a continuous absorbent macrostructure layer 71 and asubstrate layer comprising a plurality of capillary elements or strands73 of a substrate material having a length, bonded to the absorbentmacrostructure layer 71.

An absorbent composite according the present invention can also comprisea non-continuous composite structure having a substantial number of openvoids or spaces penetrating at least partially through the plane of theabsorbent composites. Preferably, such structures are formed fromcontinuous absorbent structures described herein. Such non-continuousabsorbent structures are disclosed and claimed in co-pending,commonly-assigned U.S. patent application Ser. No. 08/142,259, filedOct. 22, 1993, Attorney Docket No. JA-67U. Examples of non-continuouscomposites are shown in FIGS. 8 and 9.

In a preferred embodiment, the voids or spaces extend completely throughthe absorbent composite. An embodiment of a non-continuous absorbentcomposite structure comprises a plurality of interconnected strandscomprising at least one absorbent macrostructure and at least onesubstrate attached to the absorbent macrostructure. The macrostructurecomprises a multiplicity of interconnected absorbent gelling particles.The absorbent gelling particles are preferably bonded together to formthe strands. The strands are separated by a plurality of voids or spacesformed in the plane of the composite, in a preferred embodiment, thestrands are directly interconnected to form the net-like structure shownin FIG. 9. In another embodiment, the strands are directly andirregularly interconnected to form a irregular net-like shape.

Upon wetting of the absorbent macrostructure, and swelling of theabsorbent gelling particles in the absorbent macrostructures, theabsorbent macrostructure can expand into the voids. Therefore, planarexpansion of the absorbent composite can be minimized. Preferably, theplanar expansion, upon wetting and swelling of the absorbent gellingparticles, is less than 25% of the planar area prior to wetting, morepreferably less than 15%. Most preferably, planar expansion of theabsorbent composite upon wetting and swelling of the absorbent gellingparticles is substantially eliminated.

An absorbent composite according the present invention can also besemi-continuous. Preferably, such structures are formed fromnon-continuous absorbent structures described herein. Thesesemi-continuous absorbent structures are disclosed and claimed inco-pending, commonly-assigned U.S. patent application Ser. No.08/142,259, filed (Oct. 22, 1993), Attorney Docket No. JA-67U Asemi-continuous composite structure of the present invention comprisesat least one continuous layer selected from a substrate layer or anabsorbent macrostructure layer, preferably a substrate layer, and atleast one non-continuous absorbent macrostructure layer comprising aplurality of open voids or spaces penetrating completely therethrough.Preferably, the non-continuous absorbent macrostructure layer is formedfrom a plurality of strands of the absorbent macrostructure. Thenon-continuous absorbent macrostructure layer is associated with,preferably attached or bonded to, the continuous layer to form asemi-continuous absorbent composite structure, whereby interconnectionof the strands in the non-continuous absorbent macrostructure layer canbe made. Some examples of the semi-continuous structure are shown inFIGS. 10, 11 and 12. In another embodiment, irregularly interconnected,strands of absorbent macrostructure are attached or bonded to, thecontinuous layer to form a semi-continuous absorbent composite.

In a preferred embodiment, the semi-continuous composite structure ofthe present invention can comprise at least one continuous substrateattached to a surface of a plurality of interconnected strands. Theinterconnected strands comprise at least one absorbent macrostructureand at least one discrete substrate attached to the absorbentmacrostructure.

Porous Absorbent Macrostructure Layer

The porous absorbent macrostructure layer of the present inventioncomprises interconnected absorbent gelling particles havingintermolecular crosslinked absorbent molecules. The surfaces of theparticles are at least partially crosslinked, preferably completelycrosslinked with a crosslinking agent. More preferably, in theseparticles, at least a portion of the surface has a level of crosslinkingbetween the absorbent molecules that is higher than the remainingportion of the particle. Preferably, crosslinking agents for absorbentmolecules are used to form the higher level of crosslinking at thesesurfaces of the particles. In preferred embodiments, a cationicamino-epichlorohydrin adduct is used to chemically effect thehigher-level crosslinking of the surface portions of the particles. Theamino-epichlorohydrin adducts preferred for use herein as bonding agentsare commercially marketed by Hercules Inc. under the trade name Kymene®Especially useful are Kymene® 557H, Kymene® 557LX and Kymene® 557 Plus.These are the epichlorohydrin adducts of polyamide-polyamine, which isthe reaction product of diethylenetriamine and adipic acid. They aretypically marketed in the form of aqueous solutions of the cationicresin material containing from about 10% to about 33% by weight of theresin active.

The particles of the macrostructure are preferably attached to otheradjacent absorbent gelling particles by their surfaces. Any means forinterconnecting the particles can be used such that a fluid-stablemacrostructure of interconnected particles is formed. For example, theinterconnecting means can comprise a variety of chemical, physical, andadhesive agents. In a preferred embodiment, water-soluble and wetstrength polyamide resins are used for interconnecting the particles.Adhesive means for interconnecting the particles can comprise glues,adhesives such as those which are well known in the art. Preferably, theadjacent interconnected particles are bonded together, more preferablybonded through the higher-level crosslinked surface portions. Apreferred bonding material is a crosslinking agent for the polymermaterial of the particles. A particular preferred bonding materials isthe cationic amino-epichlorohydrin adduct such as Kymene®.

Porous, absorbent macrostructures used in the absorbent compositesaccording to the present invention are structures capable of absorbinglarge quantities of liquids such as water and/or body exudates (e.g.,urine or menses) and then retaining such liquids under moderatepressures. Because of the particulate nature of the precursor particles,the macrostructure has pores between adjacent precursor particles. Thesepores are interconnected by intercommunicating channels such that themacrostructure is liquid permeable (i.e., has capillary transportchannels).

Due to the crosslinking of the absorbent polymers in the interconnectedsurface portions of adjacent, interconnected gelling particles, theresultant absorbent macrostructure has good structural integrity,increased liquid acquisition and distribution rates, and minimalgel-blocking characteristics. When contacted with liquid, the absorbentmacrostructure absorbs such liquids into the pores between the precursorparticles, and then imbibes such liquids into the particles, whereby theabsorbent macrostructure swells generally isotropically even undermoderate confining pressures. Isotropic swelling is used herein to meanthat the macrostructure swells generally equally in all directions whenwetted. Isotropic swelling is an important property of themacrostructure because the absorbent gelling particles and theirassociated pores are able to maintain their relative geometry andspatial relationships even when swollen, such that the existingcapillary channels are maintained, if not enlarged, during use. (Thepores and the absorbent gelling particles get larger during swelling.)Thus, the macrostructure can imbibe and/or transport through itselfadditional loadings of liquid while not gel blocking.

An indication that crosslink bonds are being formed at the surface ofthe absorbent gelling particles (hereinafter also referred to asprecursor particles) is that the resultant macrostructures are fluid(i.e., liquid) stable. "Fluid stable" is used herein to mean amacrostructure comprising an aggregate of interconnected particles thatremains substantially intact (i.e., most of the previously independentcomponent precursor particles remain bonded together) upon contact withor swelling (with and/or without stress) in an aqueous fluid. While thisdefinition of fluid stability recognizes that most, preferably all, ofthe precursor particles remain bonded together, some of the precursorparticles can dissociate themselves from the macrostructure if, forexample, other particles have been subsequently water agglomerated ontoit.

Fluid stability is an important feature of the absorbent macrostructurelayers in the present invention because it allows the aggregate tomaintain its relative structure in both the dry and swollen states, andbecause it immobilizes component precursor particles. In an end productsuch as an absorbent member or an absorbent article, fluid stability isbeneficial in reducing gel blocking since precursor particles remainaggregated even when contacted with liquid, and allows one to usepreviously independent fine particles in an aggregate form to increasethe rate of fluid uptake of the resultant macrostructure withoutintroducing the element of gel blocking.

Fluid stability can be measured in an aggregate macrostructure by a twostep process. The initial dynamic response of the aggregatemacrostructure upon contact with the aqueous fluid is observed and thenthe fully swollen equilibrium condition of the aggregate macrostructureis observed. A test method for determining fluid stability based onthese criteria is hereafter described in the Test Methods section.

As used herein, the term "macrostructure" means a structure having acircumscribed volume when substantially dry (i.e., circumscribed dryvolume) of at least about 0.008 mm³, preferably at least about 10.0 mm³,more preferably at least about 100 mm³, most preferably at least about500 mm³. Typically, the macrostructures of the present invention willhave a circumscribed dry volume much greater than about 500 mm³. Inpreferred embodiments of the present invention, the macrostructures havea circumscribed dry volume of between about 1000 mm³ and about 100,000mm³.

While the macrostructures used in absorbent composites of the presentinvention can have a number of shapes and sizes, they are typically inthe form of sheets, films, cylinders, blocks, spheres, fibers,filaments, or other shaped elements. The macrostructures will generallyhave a thickness or diameter between about 0.2 mm and about 10.0 mm.Preferably for use in absorbent products, the macrostructures are in theform of a sheet. The term "sheet" as used herein describesmacrostructures having a thickness at least about 0.2 mm. The sheetswill preferably have a thickness between about 0.5 mm and about 10 mm,typically from about 1 mm to about 3 mm.

As shown in FIGS. 13 through 16, the porous, absorbent macrostructuresused in the absorbent composite of the present invention compriseaggregates of interconnected particles. These aggregates ofinterconnected particles usually comprise about 8 or more previouslyindependent precursor particles. For preferred circumscribed dry volumesand sizes of the individual precursor particles used herein, theseaggregates of interconnected particles typically are formed from about100,000 or more individual precursor particles. These individualprecursor particles can comprise granules, pulverulents, spheres,flakes, fibers, aggregates or agglomerates.

As can be especially seen in FIGS. 13 and 14, the individual precursorparticles can have a variety of shapes, such as cubic, rod-like,polyhedral, spherical, rounded, angular, irregular, porous-on-surface,randomly-sized irregular shapes, e.g., pulverulent products of grindingor pulverising steps, or shapes having a large greatestdimension/smallest dimension ratio so as to be needle-like, plate-like,flake-like, or fiber-like. An example of porous-on-surface precursorparticles is disclosed in U.S. Pat. No. 5,118,719, issued Jun. 2, 1992,which is herein incorporated by reference.

As particularly shown in FIGS. 15 and 16, the aggregate ofinterconnected particles comprising the macrostructures of the presentinvention are formed, in essence, by connecting together of adjacentparticles. The interconnection of adjacent particles is essentially madeby the polymeric material that is present in the surface portions ofthese particles. Treatment of the precursor particles comprisescontacting portions of their surfaces with a crosslinking agent, and aswelling agent, preferably water. In preferred embodiments, aplasticizer is also used, most preferably in combination with thetreatment agent, to improve the flexibility and integrity of the porousabsorbent macrostructure. When these precursor particles are treated atportions of the surface of the particles, and physically associated asdescribed hereafter, the polymer material present in the surfaceportions of these particles becomes sufficiently plastic (softened) andcohesive (e.g., sticky) such that adjacent particles cohesively adheretogether. When the crosslinking agent reacts with the polymer materialof the interconnected surface portions of the particles, theinterconnected portions become set, strong, and fast absorbing, therebyforming the porous absorbent macrostructure.

The quantity of the absorbent particles comprised in the absorbentmacrostructure layer, or the thickness of the sheet of the absorbentmacrostructure layer, can be varied to provide the absorbent compositewith different amounts of absorbency. In preferred embodiments of anabsorbent composite in the forms of a sheet, the basis weight of anabsorbent macrostructure layer (expressed as weight of absorbentmacrostructure per unit area of the absorbent macrostructure layer) isfrom about 100 g/m² to about 1500 g/m² in average, more preferably fromabout 250 g/m² to about 1200 g/m² in average. In addition, the absorbentmacrostructure layer preferably has a density of from about 0.6 g/cc toabout 1.1 g/cc.

The percent void volume (i.e., the percent of volume of themacrostructure that comprises the pores and the channels) has a minimumvalue for a given precursor particle size distribution. In general, whenthe precursor particle size distribution is more narrow, the percentvolume void is higher. Thus, it is preferred, so that the precursorparticles have a relatively narrow particle size distribution, toprovide a higher percent volume void in a densified state. Also, ingeneral, when the precursor particle size is larger, the percent voidvolume is higher.

The absorbent macrostructure can also comprise a plurality of absorbentgelling particle layers each comprising absorbent gelling particles. Theplurality of absorbent gelling particle layers have substantiallydifferent particle sizes at least in two adjacent particle layers.Preferably, the mass average particle sizes of the plurality ofabsorbent gelling particle layers are changed with successive particlelayers. In one preferred embodiment shown in FIG. 17A, the absorbentmacrostructure 71 a comprises a plurality of layers of absorbent gellingparticles where the mass average particle size of the layered particlesis gradually reduced in the direction away from the substrate layer 72.On the other hand, in another embodiment shown in FIG. 17B, themacrostructure layer 71b comprises a plurality of layers of absorbentgelling particles where the mass average particle size of the layeredparticles is gradually increased in the direction away from thesubstrate layer 72. It is believed that the layering of particles ofincreasing (or decreasing) particle size in the porous macrostructurescan provide benefits in fluid acquisition, distribution and storage. Forexample, in a macrostructure layer which has upper most particle layerswith particles relatively larger than those in the lower most layers,the larger void areas between adjacent larger particles in the upperlayers have a relatively greater porosity and fluency for the liquids,allowing a substantial portion of the fluid to pass therethrough to thelower layers. In the lower layers, because of the smaller pores and voidspaces, the liquids are readily acquired and absorbed into the smallerabsorbent particles, which then begin to swell. The larger particles inthe upper most layer remain available to acquire and absorb additionaldeposits of liquid. Particularly in the case of absorbent diapers, wheremultiple depositions of liquids are expected, the layering of particlesby size can optimize the absorbent capacity of the absorbent material.

In a similar manner, an absorbent macrostructure can comprise aplurality of particle layers wherein the absorbent gelling particles ofany two layers can have different absorbent gelling particle properties.These different absorbent gelling particle properties can include, forexample, different liquid absorption rate, different liquid absorptioncapacity, different particle shape, different particle gel strength, orcombinations of these different properties. As in the case of absorbentgelling particle size, the successive layers of absorbent gellingparticles can be ordered in terms of these absorbent gelling particleproperties. By way of example, an absorbent macrostructure can be madeby having faster absorbent gelling particles in the bottom-most layers,adjacent to the substrate, and slower absorbent gelling particles nearthe surface.

In an alternate embodiment, layers of absorbent gelling particles can beseparated by a layer of non-absorbent-gelling material, preferably inparticulate form. Such non-absorbent gelling material can includeabsorbent fibers or other forms as described hereinafter, or can includeparticulate material which can provide other functions, such as odorcontrol.

The absorbent macrostructure layer can optionally comprisenon-absorbent-gelling materials, such as non-absorbent-gelling fibers.Such fiber material can be used as reinforcing members in themacrostructure layers of the present invention, as well as aco-absorbent with the absorbent gelling particles. Any type of fibermaterial which is suitable for use in conventional absorbent productscan be used in the macrostructures herein. Specific examples of suchfiber material include cellulose fibers, modified cellulose fibers,rayon, polypropylene, and polyester fibers such as polyethyleneterephthalate (DACRON), hydrophilic nylon (HYDROFIL), and the like.Examples of other fiber materials for use in the present invention inaddition to some already discussed are hydrophilized hydrophobic fibers,such as surfactant-treated or silica-treated thermoplastic fibersderived, for example, from polyolefins such as polyethylene orpolypropylene, polyacrylics, polyamides, polystyrenes, polyurethanes andthe like. In fact, hydrophilized hydrophobic fibers which are in and ofthemselves not very absorbent and which, therefore, do not provide websof sufficient absorbent capacity to be useful in conventional absorbentstructures, are suitable for use in the macrostructure layers of thepresent invention by virtue of their good wicking properties. This isbecause, in the macrostructures herein, the wicking propensity of thefibers is as important, if not more important, than the absorbentcapacity of the fiber material itself due to the high rate of fluiduptake and lack of gel blocking properties of the macrostructure layersin the present invention. Synthetic fibers are generally preferred foruse herein as the fiber component of the macrostructure layers. Mostpreferred are polyolefin fibers, preferably polyethylene fibers.

Other cellulosic fiber materials which can be useful in certainmacrostructure layers herein are chemically stiffened cellulosic fibers.Preferred chemically stiffened cellulosic fibers are the stiffened,twisted, curled cellulosic fibers which can be produced by internallycrosslinking cellulose fibers with a crosslinking agent. Suitablestiffened, twisted, curled cellulose fibers useful as the hydrophilicfiber material herein are described in greater detail in U.S. Pat. No.4,888,093 (Dean et al), issued Dec. 19, 1989; U.S. Pat. No. 4,889,595(Herron et al), issued Dec. 26, 1989; U.S. Pat. No. 4,889.596 (Schoggenet al), issued Dec. 26, 1989; U.S. Pat. No. 4,889,597 (Bourbon et al),issued Dec. 26, 1989; and U.S. Pat. No. 4,898,647 (Moore et al), issuedFeb. 6, 1990, all of which are incorporated by reference.

In another preferred embodiment, the absorbent macrostructure layer canoptionally comprise cellulose foam particles (or granules) mixed withthe absorbent gelling particles. Preferably, the cellulose foamparticles have an average volume of at least about 0.1 mm³, morepreferably from about 1.0 mm³ to about 125 mm³.

As used herein, the term "hydrophilic" describes fibers or the surfacesof fibers which are wetted by the aqueous liquids deposited onto thefibers (i.e., if water or aqueous body fluid readily spreads on or overthe surface of the fiber without regard to whether or not the fiberactually imbibes fluid or forms a gel). The state of the art respectingwetting of materials allows definition of hydrophobicity (and wetting)interms of contact angles and the surface tension of the liquids andsolids involved. This is discussed in detail in the American ChemicalSociety Publication entitled "Contact Angle, Wettability, and Adhesionedited by Robert F. Gould and copyrighted in 1964. A fiber or surface ofa fiber is said to be wetted by a liquid either when the contact anglebetween the liquid and the fiber or surface is less than 90° or when theliquid will tend to spread spontaneously across the surface of thefiber; both conditions normally coexisting.

Other materials to provide various additional functionality. Suchadditional functionality can include porosity, permeability, odorcontrol, wetness indication, structural flexibility, and structuralintegrity. Non-limiting examples of such other materials include :filler material, such as silica; wetness indicators; and odor controlagents such as those disclosed in U.S. Pat. No. 5,161,686.

The absorbent macrostructure layer typically comprises from about 50% toabout 100%, preferably from about 70% to about 100%, and more preferablyabout 90% a more by weight of absorbent gelling particles.

C. Absorbent Precursor Particles

The macrostructures used in the present invention are formed frompolymer materials capable of absorbing large quantities of liquids.(Such polymer materials are commonly referred to as "hydrogel","hydrocolloid", or "superabsorbent" materials.) The macrostructurespreferably comprise substantially water-insoluble, absorbenthydrogel-forming, polymer material. The specific polymer materials willbe discussed herein with respect to those forming the absorbent gellingparticles (hereinafter also referred to as "precursor particles").

Although the precursor particles can have a size varying over a widerange, specific particle size distributions and sizes are preferred. Forpurposes of the present invention, particle size is defined forprecursor particles that do not have a large greatest dimension/smallestdimension ratio such as fibers (e.g., granules, flakes, or pulverulents)as the dimension of a precursor particle which is determined by sievesize analysis. Thus, for example, a precursor particle that is retainedon a standard #30 sieve with 600 micron openings is considered to have aparticle size greater than 600 microns, a precursor particle that passesthrough the #30 sieve with 600 micron openings and is retained on astandard #35 sieve with 500 micron openings is considered to have aparticle size between 500 and 600 microns, and a precursor particle thatpasses through a #35 sieve with 500 micron openings is considered tohave a particle size less than 500 microns. In preferred embodiments ofthe present invention, the precursor particles will generally range insize from about 1 micron to about 2000 microns, more preferably fromabout 20 microns to about 1000 microns.

Further, for purposes of this invention, the mass average particle sizeof the precursor particles is important in determining thecharacteristics and properties of the resultant macrostructures. Themass average particle size of a given sample of precursor particles isdefined as the particle size which is the average particle size of thesample on a mass basis. A method for determining the mass averageparticle size of a sample is described hereinafter in the Test Methodssection. The mass average particle size of the precursor particles willgenerally be from about 20 microns to about 1500 microns, morepreferably from about 50 microns to about 1000 microns, most preferablyfrom about 50 microns to about 800 microns. In especially preferredembodiments, the mass average particle sizes is from about 100 micronsto about 250 microns. The particles can be substantially uniform in sizeand shape, or can be randomly or ordered in size and shape. In anexemplary embodiment, at least about 95% by weight of the precursorparticles have a particle size between about 150 microns and about 300microns. In an alternative embodiment, at least about 95% by weight ofthe precursor particles have a particle size between about 90 micronsand about 180 microns. Narrow precursor particle size distributions arepreferred because they result in a higher porosity macrostructure due tothe higher void fraction when densified versus broader precursorparticle size distributions with equivalent mass average particle sizes.

The particle size of materials having a large greatestdimension/smallest dimension such as fibers is typically defined bytheir largest dimension. For example, if absorbent, polymeric fibers(i.e. superabsorbent fibers) are used in the macrostructures, the lengthof the fibers is used to define the "particle size." (The denier and/orthe diameter of the fibers can also be specified. ) In exemplaryembodiments of the present invention, the fibers have a length greaterthan about 5 mm, preferably between about 10 mm and about 100 mm, morepreferably between about 10 mm and about 50 mm.

The precursor particles comprise substantially water-insoluble,absorbent hydrogel-forming, polymer material having a multiplicity ofanionic, functional groups, such as sulfonic acid, and more typicallycarboxy, groups. Examples of polymer materials suitable for use as theprecursor particles herein include those which are prepared frompolymerizable, unsaturated, acid-containing monomers. Thus, suchmonomers include the olefinically unsaturated acids and anhydrides whichcontain at least one carbon to carbon olefinic double bond. Morespecifically, these monomers can be selected from olefinicallyunsaturated carboxylic acids and acid anhydrides, olefinicallyunsaturated sulfonic acids, and mixtures thereof.

Some non-acid monomers can also be included, usually in minor amounts,in preparing the precursor particles herein. Such non-acid monomers caninclude, for example, the water-soluble or water-dispersible esters ofthe acid-containing monomers, as well as monomers which contain nocarboxylic or sulfonic acid groups at all. Optional non-acid monomerscan thus include monomers containing the following types of functionalgroups: carboxylic acid or sulfonic acid esters, hydroxyl groups,amide-groups, amino groups, nitrile groups and quaternary ammonium saltgroups. These non-acid monomers are well-known materials and aredescribed in greater detail, for example, in U.S. Pat. No. 4,076,663(Masuda et al), issued Feb. 28, 1978, and in U.S. Pat. No. 4,062,817(Westerman), issued Dec. 13, 1977, both of which are incorporated byreference.

Olefinically unsaturated carboxylic acid and carboxylic acid anhydridemonomers include the acrylic acids typified by acrylic acid itself,methacrylic acid, ethacrylic acid, a-chloroacrylic acid, a-cyanoacrylicacid, b-methylacrylic acid (crotonic acid), a-phenylacrylic acid,b-acryloxypropionic acid, sorbic acid, a-chlorosorbic acid, angelicacid, cinnamic acid, p-chloro cinnamic acid, b-sterylacrylic acid,itaconic acid, citroconic acid, mesaconic acid, glutaconic acid,aconitic acid, maleic acid, fumaric acid, tricarboxyethylene and maleicacid anhydride.

Olefinically unsaturated sulfonic acid monomers include aliphatic oraromatic vinyl sulfonic acids such as vinylsulfonic acid, allyl sulfonicacid, vinyltoluene sulfonic acid and styrene sulfonic acid; acrylic andmethacrylic sulfonic acid such as sulfoethyl acrylate, sulfoethylmethacrylate, sulfopropyl acrylate, sulfopropyl methacrylate,2-hydroxy-3-methacryloxy propyl sulfonic acid and2-acrylamide-2-methylpropane sulfonic acid.

Preferred polymer materials for use in the present invention containcarboxy groups. These polymers include hydrolyzed starch-acrylonitrilegraft copolymers, partially neutralized starch-acrylonitrile graftcopolymers, starch acrylic acid graft copolymers, partially neutralizedstarch-acrylic acid graft copolymers, saponified vinyl acetate-acrylicester copolymers, hydrolyzed acrylonitrile or acrylamide copolymers,slightly network crosslinked polymers of any of the foregoingcopolymers, partially neutralized polyacrylic acid, and slightly networkcrosslinked polymers of partially neutralized polyacrylic acid. Thesepolymers can be used either solely or in the form of a mixture of two ormore different polymers. Examples of these polymer materials aredisclosed in U.S. Pat. No. 3,661,875, U.S. Pat. No. 4,076,663, U.S. Pat.No. 4,093,776, U.S. Pat. No. 4,666,983, and U.S. Pat. No. 4,734,478.

Most preferred polymer materials for use in making the precursorparticles are slightly network crosslinked polymers of partiallyneutralized polyacrylic acids and starch derivatives thereof. Mostpreferably, the precursor particles comprise from about 50% to about95%, preferably about 75%, neutralized, slightly network crosslinked,polyacrylic acid (i.e. poly (sodium acrylate/acrylic acid)). Asdescribed above, the precursor particles are preferably made frompolymer materials that are slightly network crosslinked. Networkcrosslinking serves to render the polymer materials from which theprecursor particles are made substantially water-insoluble and, in part,determines the absorptive capacity and extractable polymer contentcharacteristics of the precursor particles and the resultantmacrostructures. Processes for network crosslinking the polymers andtypical network crosslinking agents are described in greater detail inthe hereinbefore-referenced U.S. Pat. No. 4,076,663.

The individual precursor particles can be formed in any conventionalmanner. Typical and preferred processes for producing the individualprecursor particles are described in U.S. Pat. No. Re. 32,649 (Brandt etal), issued Apr. 19, 1988, U.S. Pat. No. 4,666,983 (Tsubakimoto et al),issued May 19, 1987, and U.S. Pat. No. 4,625.001 (Tsubakimoto et al),issued Nov. 25, 1986, all of which are incorporated by reference.Preferred methods for forming the precursor particles are those thatinvolve aqueous solution or other solution polymerization methods. Asdescribed in the above-referenced U.S. Pat. No. Re. 32,649, aqueoussolution polymerization involves the use of an aqueous reaction mixtureto carry out polymerization to form the precursor particles. The aqueousreaction mixture is then subjected to polymerization conditions whichare sufficient to produce in the mixture, substantially water-insoluble,slightly network crosslinked polymer material. The mass of polymermaterial thereby formed is then pulverized or chopped to form theindividual precursor particles.

More specifically, the aqueous solution polymerization method forproducing the individual precursor particles comprises the preparationof an aqueous reaction mixture in which to carry out polymerization toform the desired precursor particles. One element of such a reactionmixture is the acid group-containing monomer material which will formthe "backbone" of the precursor particles to be produced. The reactionmixture will generally comprise about 100 parts by weight of the monomermaterial. Another component of the aqueous reaction mixture comprises anetwork crosslinking agent. Network crosslinking agents useful informing the precursor particles are described in more detail in theabove-referenced U.S. Pat. No. Re. 32,649, U.S. Pat. No. 4,666,983, andU.S. Pat. No. 4,625,001. The network crosslinking agent will generallybe present in the aqueous reaction mixture in an amount of from about0.001 mole percent to about 5 mole percent based on the total moles ofmonomer present in the aqueous mixture (about 0.01 to about 20 parts byweight, based on 100 parts by weight of the monomer material). Anoptional component of the aqueous reaction mixture comprises a freeradical initiator including, for example, peroxygen compounds such assodium, potassium, and ammonium persulfates, caprylyl peroxide, benzoylperoxide, hydrogen peroxide, cumene hydroperoxides, tertiary butyldiperphthalate, tertiary butyl perbenzoate, sodium peracetate, sodiumpercarbonate, and the like. Other optional components of the aqueousreaction mixture comprise the various non-acidic co-monomer materialsincluding esters of the essential unsaturated acidic functionalgroup-containing monomers or other co-monomers containing no carboxylicor sulfonic acid functionalities at all.

The aqueous reaction mixture is subjected to polymerization conditionswhich are sufficient to produce in the mixture substantiallywater-insoluble, absorbent, hydrogel-forming, slightly networkcrosslinked polymer materials. The polymerization conditions are alsodiscussed in more detail in the three above-referenced patents. Suchpolymerization conditions generally involve heating (thermal activationtechniques) to a polymerization temperature from about 0° C. to about100° C. , more preferably from about 5° C. to about 40° C.Polymerization conditions under which the aqueous reaction mixture ismaintained can also include, for example, subjecting the reactionmixture, or portions thereof, to any conventional form of polymerizationactivating irradiation. Radioactive, electronic, ultraviolet, orelectromagnetic radiation are alternative conventional polymerizationtechniques.

The acid functional groups of the polymer materials formed in theaqueous reaction mixture are also preferably neutralized. Neutralizationcan be carried out in any conventional manner which results in at leastabout 25 mole percent, and more preferably at least about 50 molepercent, of the total monomer utilized to form the polymer materialbeing acid group-containing monomers that are neutralized with asalt-forming cation. Such salt-forming cations include, for example,alkali metals, ammonium, substituted ammonium and amines as discussed infurther detail in the above-references U.S. Pat. No. Re. 32,649. Whileit is preferred that the precursor particles be manufactured using anaqueous solution polymerization process, it is also possible to carryout the polymerization process using multi-phase polymerizationprocessing techniques such as inverse emulsion polymerization or inversesuspension polymerization procedures. In the inverse emulsionpolymerization or inverse suspension polymerization procedures, theaqueous reaction mixture as hereinbefore described is suspended in theform of tiny droplets in a matrix of a water-immiscible, inert organicsolvent such as cyclohexane. The resultant precursor particles aregenerally spherical in shape. Inverse suspension polymerizationprocedures are described in greater detail in U.S. Pat. No. 4,340,706(Obaysashi et al), issued Jul. 20, 1982, U.S. Pat. No. 4,506,052(Flesher et al), issued Mar. 19, 1985, and U.S. Pat. No. 4,735,987(Morita et al), issued Apr. 5, 1988, all of which are incorporated byreference.

The precursor particles are preferably substantially dry. The term"substantially dry" is used herein to mean that the precursor particleshave a liquid content, typically water or other solution content, lessthan about 50%, preferably less than about 20%, more preferably lessthan about 10%, by weight of the precursor particles. Most preferably,the liquid content of the precursor particles is in the range of fromabout 0.01% to about 5% by weight of the precursor particles. Theindividual precursor particles can be dried by any conventional methodsuch as by heating. Alternatively, when the precursor particles areformed using an aqueous reaction mixture, water can be removed from thereaction mixture by azeotropic distillation. The polymer-containingaqueous reaction mixture can also be treated with a dewatering solventsuch as methanol. Combinations of these drying procedures can also beused. The dewatered mass of polymer material can then be chopped orpulverized to form substantially dry precursor particles ofsubstantially water-insoluble, absorbent, hydrogel-forming, polymermaterial.

Preferred precursor particles of the present invention are those whichexhibit a high absorptive capacity so that the resultant macrostructureformed from such precursor particles also has a high absorptivecapacity. Absorptive capacity refers to the capacity of a given polymermaterial to absorb liquids with which it comes into contact. Absorptivecapacity can vary significantly with the nature of the liquid beingabsorbed and with the manner in which the liquid contacts the polymermaterial. For purposes of this invention, Absorptive Capacity is definedin terms of the amount of Synthetic Urine (as hereinafter defined)absorbed by any given polymer material in terms of grams of SyntheticUrine per gram of polymer material in a procedure hereinafter defined inthe Test Methods section. Preferred precursor particles of the presentinvention are those which have an Absorptive Capacity of at least about20 grams, more preferably at least about 25 grams, of Synthetic Urineper gram of polymer material. Typically, the polymer materials of theprecursor particles herein have an Absorptive Capacity of from about 20grams to about 70 grams of Synthetic Urine per gram of polymer material.Precursor particles having this relatively high absorptive capacitycharacteristic produce macrostructures that are especially useful inabsorbent products, absorbent members, and absorbent articles since theresultant macrostructures formed from such precursor particles can, bydefinition, hold desirably high amounts of discharged body exudates suchas urine.

While all of the precursor particles are preferably formed from the samepolymer material with the same properties, this need not be the case.For example, some precursor particles can comprise a starch-acrylic acidgraft copolymer while other precursor particles can comprise a slightlynetwork crosslinked polymer of partially neutralized polyacrylic acid.Further, the precursor particles can vary in size, shape, absorptivecapacity, or any other property or characteristic. In a preferredembodiment of the present invention, the precursor particles consistessentially of slightly network crosslinked polymers of partiallyneutralized polyacrylic acid, each precursor particle having similarproperties.

In another embodiment of the present invention, the precursor particlescan themselves be crosslinked at least at a portion of, preferablysubstantially all of, their surfaces, prior to forming the precursorparticles into an absorbent macrostructure. The surface crosslinking ofprecursor particles can be made by any of the crosslinking agentsdescribed hereinafter. Preferred crosslinking agents preferably haverelatively large molecular size, and are preferably cationic. Such acrosslinking agent is unable to penetrate inside the absorbentparticles, and therefore can only react with polymer material at thesurface thereof effectively. Most preferably, the crosslinking agent isa cationic amino-epichlorohydrin adduct.

D. Crosslinking Agent

A crosslinking agent is used to crosslink the polymer material of theprecursor particles of the absorbent macrostructure. A suitablecrosslinking agent can be a nonionic crosslinking agents described inU.S. Pat. No. 5,102,597 (Roe et al), issued Apr. 7, 1992. These nonioniccrosslinking agents include polyhydric alcohols (e.g., glycerol),polyaziridine compounds (e.g., 2,2-bishydroxymethylbutanoltris[3-(1-aziridine) propionate]), haloepoxy compounds (e.g.,epicholorhydrin), polyaldehyde compounds (e.g., glutaraldehyde),polyamine compounds (e.g., ethylene amine), and polyisocyanate compounds(e.g., 2,4-toluene diisocyanate), preferably glycerol.

Preferred crosslinking agents are those which primarily providecrosslinking at portions of the surface of the absorbent precursorparticles. Such crosslinking agents preferably have relatively largemolecular size, and are preferably cationic. As a result, it isbelieved, such a crosslinking agent is unable to penetrate inside theabsorbent particles, and therefore can only react with polymer materialat the surface thereof effectively. It is possible that some such largercrosslinking agent can penetrate into the particle when the particle isswelled via the swelling agent.

Another preferred crosslinking agent is one which reacts very rapidlywith the anionic, typically carboxy functional groups of the polymermaterial of the absorbent particles, even at a room temperature range(e.g., at from about 13° C. to about 33° C. ). As a result, fairlymodest levels (e.g., as low as about 1% by weight of the particles) ofsuch crosslinking agent are required to provide effective surfacecrosslinking of the polymer material present in the absorbent precursorparticles.

A preferred crosslinking agent of the present invention, however, is anadduct of epichlorohydrin with certain types of monomeric or polymericamines. These amino-epichlorohydrin adducts react with the polymermaterial of the absorbent precursor particles, and in particular theanionic, typically carboxy, functional groups of these polymer materialsto form a covalent, ester-type bond. In other words, theamino-epichlorohydrin adduct serves to crosslink the polymer materialpresent in the absorbent precursor particles. (The portions of theabsorbent particle containing polymer material that has been effectivelycrosslinked with the amino-epichlorohydrin adduct swell less in thepresence of aqueous body fluids relative to the other uncrosslinkedportions of the particle.) Such cationic amino-epichlorohydrin adduct,especially a polymeric resin version, is relatively large such thatpreferential surface crosslinking is achieved. Such adduct with itscationic functional groups (e.g., azetedinium groups) can react rapidlywith the polymer material at the room temperature range of preferablyfrom about 13° C. to about 33° C., more preferably from about 18° C. toabout 28° C., most preferably about 23° C.

As used herein, "cationic amino-epichlorohydrin adduct" refers to thereaction product between epichlorohydrin and a monomeric or polymericamine such that the resulting reaction product has at least two cationicfunctional groups. These adducts can be in the form of monomericcompounds (e.g., the reaction product of epichlorohydrin and ethylenealiamine), or can be in polymeric form (e.g., the reaction productbetween epichlorohydrin, and polyamide-polyamines orpolyethyleneimines). The polymeric versions of these cationicamino-epichlorohydrin adducts are typically referred to as "resins."

One type of amino compound which can be reacted with epichlorohydrin toform adducts useful in the present invention comprises monomeric di-,tri- and higher amines having primary or secondary amino groups in theirstructures. Examples of useful diamines of this type includebis-2-aminoethyl ether, N,N-dimethylethylenediamine, piperazine, andethylenediamine. Examples of useful triamines of this type includeN-aminoethyl piperazine, and dialkylene triamines such asdiethylenetriamine, and dipropylenetriamine.

Such amine materials are reacted with epichlorohydrin to form thecationic amino-epichlorohydrin adducts useful as crosslinking agentsherein. Preparation of these adducts, as well as a more completedescription of the adducts themselves, can be found in U.S. Pat. No.4,310,593 (Gross), issued Jan. 12, 1982, and in Ross et al, J. OrganicChemistry, Vol. 29, pp. 824-826 (1964). Both of these documents areincorporated by reference.

In addition to monomeric amines, polymeric amines such aspolyethyleneimines can also be used as the amino compound. Aparticularly desirable amino compound which can be reacted withepichlorohydrin to form preferred cationic polymeric adduct resinsuseful herein comprise certain polyamide-polyamines derived frompolyalkylene polyamines and saturated C3-C10 dibasic carboxylic acids.Epichlorohydrin/polyamide-polyamine adducts of this kind arewater-soluble, thermosetting cationic polymers which are well known inthe art as wet strength resins for paper products.

In the preparation of polyamide-polyamines used to form this preferredclass of cationic polymeric resins, a dicarboxylic acid is first reactedwith a polyalkylene-polyamine, preferably in aqueous solution, underconditions such as to produce a water-soluble, long chain polyamidecontaining the recurring groups --NH(CnH2nHN)x-- CORCO-- where n and xare each 2 or more and R is the C1 to C8 alkylene group of thedicarboxylic acid.

A variety of polyalkylene polyamines including polyethylene polyamines,polypropylene polyamines, polybutylene polyamines and so on can beemployed to prepare the polyamide-polyamine, which the polyethylenepolyamines represent an economically preferred class. More specifically,preferred polyalkylene polyamines used to prepare the cationic polymericresins herein are polyamines containing two primary amine groups and atleast one secondary amine group in which the nitrogen atoms are linkedtogether by groups of the formula --CnH2n-- where n is a small integergreater than unity and the number of such groups in the molecule rangesfrom two up to, about eight and preferably up to about four. Thenitrogen atoms can be attached to adjacent carbon atoms in the group--CnH2n-- or to carbon atoms further apart, but not to the same carbonatom. Also contemplated is the use of such polyamines asdiethylenetriamine, triethylene tetramine, tetraethylenepentamine,dipropylenetriamine, and the like, which can be obtained in reasonablypure form. Of all the foregoing, the most preferred are the polyethylenepolyamines containing from two to four ethylene groups, two primaryamine groups, and from one to three secondary amine groups.

Also contemplated for use herein are polyamine precursor materialscontaining at least three amino groups with at least one of these groupsbeing a tertiary amino group. Suitable polyamines of this type includemethyl bis(3-aminopropyl)amine, methyl bis(2-aminoethyl)amine,N-(2-aminoethyl) piperazine, 4,7-dimethyltriethylenetetramine and thelike.

The dicarboxylic acids which can be reacted with the foregoingpolyamines to form the polyamide-polyamine precursors of the preferredcationic polymeric resins useful herein comprise the saturated aliphaticC3-C10 dicarboxylic acids. More preferred are those containing from 3 to8 carbon atoms, such as malonic, succinic, glutaric, adipic, and so on,together with diglycolic acid. Of these, diglycolic acid and thesaturated aliphatic dicarboxylic acids having from 4 to 6 carbon atomsin the molecule, namely, succinic, glutaric and adipic are mostpreferred. Blends of two or more of these dicarboxylic acids can also beused, as well as blends of one or more of these with higher saturatedaliphatic dicarboxylic acids such as azelaic and sebacic, as long as theresulting long chain polyamide-polyamine is water-soluble or at leastwater-dispersible.

The polyamide-polyamine materials prepared from the foregoing polyaminesand dicarboxylic acids are reacted with epichlorohydrin to form thecationic polymeric amino-epichlorohydrin resins preferred for use hereinas the crosslinking agent. Preparation of such materials is describe ingreater detail in U.S. Pat. No. 2,926,116 (Keim), issued Feb. 23, 1960,U.S. Pat. No. 2,926,154 (Keim), issued Feb. 23, 1960, and U.S. Pat. No.3,332,901 (Keim), issued Jul. 25, 1967, all of which are incorporated byreference.

The cationic polyamide-polyamine-epichlorohydrin resins preferred foruse herein as crosslinking agents are commercially marketed by HerculesInc. under the trade name Kymene®. Especially useful are Kymene® 557H,Kymene® 557LX and Kymene® 557 Plus, which are the epichlorohydrinadducts of polyamide-polyamines which are the reaction products ofdiethylenetriamine and adipic acid. They are typically marketed in theform of aqueous solutions of the cationic resin material containing fromabout 10% to about 33% by weight of the resin active.

E. Substrate layer

The substrate layer can provide a variety of functions. It can serve asa distributing means for improving the distribution of applied liquidsto be absorbed into the macrostructure layer. Preferably, the liquiddistribution properties or the substrate are substantially greater thanthose of the absorbent macrostructure, such that the composite hasimproved liquid distribution properties relative to the absorbentmacrostructure alone. In preferred embodiments, the substrate layercomprises a plurality of capillary elements having a length, preferablyarranged substantially in parallel, for improving the distribution ofthe liquid along the lengths thereof.

The substrate layer can also serve as a supporting means for theabsorbent macrostructure layer by supporting the interconnectedabsorbent particles in the absorbent macrostructure. As described above,the absorbent gelling particles are connected to at least one of theother adjacent particles through the higher level crosslinked surfaceportion. The substrate layer can support the bonds or interconnection ofthe absorbent gelling particles by resisting the forces of stress andstrain in the absorbent composite during use which might otherwise causeinterconnected particles of the absorbent macrostructure layer to breakapart. The supporting means is preferably one which has excellent wetstrength, and can impart improved wet strength and wet integrity to theabsorbent macrostructure layer: that is, the substrate is effective as asupporting means after the absorbent composite, and the substrateitself, has become wet with liquid. Support for the bonded orinterconnected gelling particles is needed especially in this situation,where the gelling particles begin to swell after absorbing liquid,thereby placing substantial strain on the interparticle connections.Such support is especially important when the absorbent composite isused in an absorbent article such as a diaper or catamenial productwhere external forces can also act upon the structure to causeinterconnected particles of the absorbent macrostructure to break apart.Therefore, the substrate layer can serve to improve both the dryintegrity and strength, and the wet integrity and strength, of theabsorbent composite.

The support function provided by a substrate can also permit less densemacrostructure layers. The less dense absorbent macrostructures have ahigher percent void volume and larger pore openings between adjacentinterconnected gelling particles, thus reducing the potential for gelblocking and reducing the stresses in the macrostructure as theparticles absorb fluid and expand.

The substrate layer can be selected from various materials known in theart such as cellulose fibers, nonwoven webs, tissue webs, foams,polyacrylate fibers, apertured polymeric webs, synthetic fibers,metallic foils, elastomers, and the like. Most such substrates can serveboth as a distributing means and a supporting means for the absorbentmacrostructure layer. Preferably, the substrate layer is comprised ofcellulosic material or a material having cellulosic functionality.Preferred substrates for use as a fluid distributing means can beselected from cellulosic materials, fibrous webs, cellulosic fibrouswebs, solid foams, cellulosic foams, and polyvinyl alcohol foams.Preferred substrates for use as a supporting means can be selected fromcellulosic materials, fibrous webs, nonwoven webs, fabrics, cellulosicfibrous webs, solid foams, cellulosic foams, and polyvinyl alcoholfoams.

The substrate layer is preferably flexible and pliable to encourage suchproperties in the resulting absorbent composite. A substrate layer canbe substantially resilient and non-stretchable, or it can be stretchableor deformable to a varying extent in response to forces exerted normalto and in the plane of the surface of the substrate.

The thickness and basis weight (weight per unit area of substrate) of asubstrate material will vary depending on the type of substrate and thedesired properties. A substrate can also comprises a plurality ofindividual sheets, or plies, of a particular substrate material, or acombination of one or more substrate layers in a laminate. As a typicalsubstrate, a Bounty® sheet has a thickness of from about 0.02 mm toabout 1.2 mm, more preferably from about 0.3 mm to about 0.8 mm, and abasis weight of from about 5 gm/m² to about 100 gm/m², more preferablyfrom about 10 gm/m² to about 60 gm/m², and most preferably from about 15gm/m² to about 40 gm/m². As another typical substrate, a cellulose foamhas a dry compressed thickness of from about 0.5 mm to about 3.0 mm,more preferably from about 0.8 mm to about 2.0 mm, a wet expandedthickness of from about 0.8 mm to about 6.0 mm, more preferably fromabout 1.0 mm to about 5.0 mm, and a basis weight of from about 50 gm/m²to about 2,000 gm/m², more preferably from about 100 gm/m² to about1,000 gm/m².

Substrates for use as support means typically have a dry tensilestrength of from about 500 gm/in to about 8,000 gm/in, though morepreferably from about 1,000 gm/in to about 3,000 gm/in, a wet tensilestrength of from about 200 gm/in to about 5,000 gm/in, though morepreferably from about 400 gm/in to about 1,000 gm/in, and a wet burststrength of from about 100 gm to about 2,000 gm, though more preferablyfrom about 200 gm to about 1,000 gm,

In preferred embodiments, the substrate layer comprises a cellulosicfibrous web such as paper toweling and paper tissue. Examples of suchcellulosic fibrous webs are disclosed in U.S. Pat. No. 3,953,638, issuedApr. 27, 1976, U.S. Pat. No. 4,469,735, issued Sep. 4, 1984, U.S. Pat.No. 4,468,428, issued Aug. 28, 1984, and U.S. Pat. No. 4,986,882, issuedJan. 22, 1991, all herein incorporated by reference. A preferred exampleof such is Bounty® paper towel, commercially marketed in the U.S. by TheProcter & Gamble Company. Another preferred example of such isKinocloth® paper tissue, commercially marketed in the U.S. and Japan byHonshu Paper Co., Ltd.. Bounty® and Kinocloth® are hydrophilic and havegood distribution and wicking properties, as well as good wet integrity.

In another preferred embodiment, the substrate layer comprises acellulosic foam. In general, a cellulosic foam will provide a higherliquid wicking rate over a longer wicking distance than a cellulosicfibrous web. Preferably, the cellulosic foam is in a compressed state soas to further improve its wicking and fluid distribution properties.Suitable cellulose foam can be made of regenerated rayon fibers bywell-known methods, such as those disclosed in European patentPublication (Publication No. 0,293,208), incorporated herein byreference. Such cellulose foams have numerous small cells, the size ofwhich affect the capillarity and absorptivity of the foam. The cellulosefoam layer will ordinarily, and preferably, expand when wet. A preferredcellulosic foam is one which has been compressed in the dry state priorto use. The average pore size of the cellulose foam layer can bedetermined by the compression. In preferred embodiments, the averagepore size of the cellulose foam layer, as measured in the dry stateafter any compression, is from about 1 micron to about 1000 microns,preferably from about 1 micron to about 200 microns, more preferablyfrom about 5 microns to about 70 microns. A preferred compressedcellulose Foam layer has a density of from about 0.1 g/cc (about 0.05g/in³) to about 0.8 g/cc (about 0.41 g/in³) and has a compressedthickness (in sheet form) of from about 2 mm to about 5 mm. In general,better wicking properties can be obtained by using a foam layer having ahigher density, or a smaller pore size. When such compressed cellulosefoam layer contacts with liquids, the pore size of the foam begins toexpand whereby the thickness of the foam layer become increased.

Absorbent foam substrates, particularly compressed cellulose foamsubstrates, are highly preferred substrates in the absorbent compositesof the present invention. In addition to having excellent dry and wetstrength and integrity, cellulose foam substrates, specifically in theform of sheets, have excellent capillarity and fluid wicking properties.When liquid such as water or body exudate is deposited onto the surfaceof an absorbent composite comprising a foam cellulose substrate, such asshown in FIG. 6, the liquid passing through the absorbent macrostructurelayer and into the cellulose foam substrate is distributed quicklyoutward toward dry foam areas in cellulose foam layer due to itscapillary suction. That is, as the cellulose foam absorbs water oraqueous liquids, the cellulose foam cell structure begins to expand.Since the dry foam areas have a cell structures which are stillcompressed and which are smaller than the cells of the wetted areas,fluids readily wick into the dry foam areas. Such cellulose foamsubstrates are characterized by excellent fluid wicking anddistribution. Specifically, such cellulose foam substrates have fastwicking ratio or speed (for example, up to at least 12 cm wickingdistance in 4 minutes in a vertical wicking test) and long wickingdistance capability (for example, from about 20 cm to about 30 cm in thefirst one hour in a vertical wicking test).

In yet another embodiment, the substrate layer can be a cellulose foamsubstrate formed by depositing cellulose foam particles (or granules).The cellulose foam particles have an average volume of at least about0.1 mm³, preferably from about 1.0 mm³ to about 125 mm³. Preferably, thecellulose foam particles are deposited and compacted on an absorbentmacrostructure layer.

A cellulose foam substrate is particular preferred when using theabsorbent composite of the present invention in an absorbent catamenialarticle. When blood is deposited onto a cellulose foam substrate layerof an absorbent composite, the cellulose foam substrate can serve toacquire the blood, filter aggregates from the blood, and distribute theremaining liquid portion of the blood to the absorbent macrostructurelayer below.

In yet another preferred embodiment, the substrate layer comprises acompressed or non-compressed polyvinyl alcohol foam. In general, suchfoam preferably has properties and structure substantially as thecellulosic foam above.

F. Bonding Between Macrostructure Layer and Substrate Layer

The bonding or interconnection between the absorbent macrostructurelayer and the substrate layer can be made by a variety of chemical,physical, and adhesive agents. In a preferred embodiment, water-solubleand wet strength polyamide resins are used for bonding the substratephysically to the absorbent macrostructure layer.

Adhesive means for attaching a substrate to an absorbent macrostructurelayer can comprise glues, adhesives such as those which are well knownin the art. Non-limiting examples of such adhesive means include FindleyH-2247 Hot Melt Adhesive, available from Findley Adhesives of Elm Grove,Wis., U.S.A., HM-6515 Hot Melt Adhesive, available from H. B. FullerCompany of St. Paul, Minn., U.S.A., Century 5227, available from CenturyAdhesives, Inc. of Columbus, Ohio, and HL-1258, available from H. B.Fuller Company of St. Paul, Minn.

In more preferred embodiments, the bonding between the substrate and theabsorbent macrostructure layer is made by a crosslinking agent capableof crosslinking the absorbent molecules of the absorbent gellingparticles in the absorbent macrostructure layer. Any crosslinking agentwhich is known in the art and is capable of crosslinking the absorbentmolecules of the absorbent gelling particles can be used as a bondingagent. A suitable crosslinking agent can be a nonionic crosslinkingagents described in U.S. Pat. No. 5,102,597 (Roe et al), issued Apr. 7,1992. These nonionic crosslinking agents include polyhydric alcohols(e.g., glycerol), polyaziridine compounds (e.g., 2,2-bishydroxymethylbutanoltris[3-(1-aziridine) propionate]), haloepoxy compounds (e.g.,epicholorhydrin), polyaldehyde compounds (e.g., glutaraldehyde),polyamine compounds (e.g., ethylene amine), and polyisocyanate compounds(e.g., 2,4-toluene diisocyanate), preferably glycerol.

In a preferred embodiment where the substrate layer comprises cellulosicmaterial or has cellulosic activity at least at the surface thereof, anamino-epichlorohydrin adduct is preferably used as a chemical bondingmeans between the cellulosic substrate and the surfaces of the absorbentgelling particles. The amino-epichlorohydrin adduct can chemically bondto carboxyl and hydroxyl groups in the cellulosic material and to thepolymer material of the absorbent precursor particles, as well as toother amino-epichlorohydrin adduct molecules. Such chemical bonding canbe hydrogen bonding, ionic/coulombic bonding, polymer entanglementbonding, and covalent bonding. In this manner, the amino-epichlorohydrinadduct can chemically bond together the substrate to the absorbentmacrostructure layer comprising the absorbent precursor particles. Theamino-epichlorohydrin adduct preferred for use herein as a bonding agentis Kymene®. Especially useful are Kymene® 557H, Kymene® 557LX andKymene® 557 Plus. These are the epichlorohydrin adducts ofpolyamide-polyamine, which is the reaction product of diethylenetriamineand adipic acid.

G. Specific Preferred Embodiments of Absorbent Composites

In the following, specific preferred embodiments are described withreference to the drawings.

(1) Continuous Absorbent Composite Embodiments

Referring to FIG. 1, continuous absorbent composite 70 comprises aporous absorbent macrostructure layer 71, and a substrate layer 72chemically bonded to the macrostructure layer. The substrate is bondedto the macrostructure layer through a bonding agent, preferably acationic amino-epichlorohydrin adduct such as Kymene®. The substratelayer is cellulosic fibrous web, such as a Bounty®-type sheet. Apreferred substrate is a double-ply of Bounty®-type sheet. Themacrostructure layer comprises a porous absorbent macrostructure asdescribed above.

Alternatively, continuous absorbent composite 70 shown in FIG. 1comprises a cellulose foam layer as substrate layer 72. The cellulosefoam layer is bonded to absorbent macrostructure layer 71 through acationic amino-epichlorohydrin adduct such as Kymene®. The cellulosefoam layer comprises cells of from about 100 microns to about 1000microns. Preferably, this cellulose foam layer is compressed to furtherimprove wicking and fluid distribution properties. The absorbentcomposite using such cellulose foam layer can be preferably used as anabsorbent core in a catamenial product.

Referring to FIG. 2, absorbent composite 70 of yet another embodimentcomprises absorbent macrostructure layer 71 formed between two substratelayers 72. One substrate layer is attached, preferably by chemicalbonding using Kymene®, to each surface 75 of absorbent macrostructurelayer. Each substrate layer is a double-ply of a Bounty®-type sheet.

Referring to FIG. 3, absorbent composite 70 of still another embodimentcomprises two absorbent macrostructure layers 71a, 71b and two substratelayers 72a, 72b. Preferably, absorbent macrostructure layer 71a has abasis weight of about 280 g/m² (about 0.18 g/in² ), which corresponds toa layer having a thickness of between one or two particle diameters (aparticle diameter being from about 150 microns to about 300 microns).Absorbent macrostructure layer 71b has a basis weight of about 560 g/m²(0.36 g/in²), which corresponds to a layer having a thickness of betweenthree or four particle diameters of the particle.

Referring to FIG. 4, absorbent composite 70 comprises three absorbentmacrostructure layers 71a, 71b, 71c and two substrate layers 72a, 72binterposed in layers 71a, 71b, and 71c alternately. Each of absorbentmacrostructure layers 71a, 71b, 71c has the basis weight of about 280g/m² (about 0.18 g/in²). Referring to FIG. 5, absorbent composite 70comprises five substrate layers 72a-72e and four absorbentmacrostructure layers 71a-71d interposed in layers 72a-72e alternately.Each of absorbent macrostructure layers 71a-71d has the basis weight ofabout 140 g/m² (about 0.09 g/in²).

Referring to FIG. 6, absorbent composite 70 comprises absorbentmacrostructure layers 71a, 71b and substrate layer 72 interposedtherebetween. Each of absorbent macrostructure layers 71a and 71b ischemically bonded to a corresponding surface 76 of substrate layer 72using Kymene®. A preferred substrate is a compressed cellulose foamlayer. The cellulose foam layer is compressed at a pressure of about 70kgf/cm² for 15 sec. in its dry state to reduce the average pore size.

FIG. 7 shows another embodiment of a continuous absorbent composite 70comprising a continuous absorbent macrostructure layer 71 and asubstrate layer which comprises a plurality of capillary elements orstrands 73 of cellulose foam having a length, bonded to themacrostructure layer 71 using Kymene®.

(2) Non-continuous Absorbent Composite Embodiments

Highly preferred absorbent composite structures of the present inventioncomprise non-continuous absorbent composites. Preferably, suchstructures are formed from continuous absorbent structures describedherein. Such non-continuous absorbent structures are disclosed andclaimed in co-pending, commonly-assigned U.S. patent application Ser.No. 08/142,259, filed (Oct. 27, 1993), Attorney Docket No. JA-67U.

One non-continuous absorbent composite 80, shown in FIG. 8, is anabsorbent composite 80 which has an absorbent macrostructure layer 81and a substrate layer 82, the composite 80 having a plurality of voids85 distributed throughout the plane of the composite.

Referring to FIG. 9, a preferred embodiment of the present invention isa non-continuous absorbent composite sheet 80 which comprises anabsorbent macrostructure layer 81 and a substrate 82 that is bonded tothe absorbent macrostructure layer 81, wherein such absorbent composite80 is in the form of a sheet having a plurality of voids or openings 85therethrough. The substrate layer is a double-ply of a Bounty®-typesheet, The substrate is chemically bonded to the absorbentmacrostructure layer through Kymene®. Preferably the non-continuousabsorbent composite 80 has an average percent void volume of from about17% to about 80%, more preferably from about 33% to about 67%. The voids85 are substantially evenly distributed across the surface of thecomposite sheet.

Another embodiment of the present invention can be a non-continuouscomposite 80 having one or more area portions which have differentaverage percent void volume. For example, a non-continuous compositesheet has three substantially equivalent portions, wherein the firstportion and the second portions each being located on opposite lateraledges of the composite sheet and having a percent void volume largerthan a percent void volume of the third portion positioned therebetween.

(3) Semi-Continuous Absorbent Composite Embodiments

Other highly preferred absorbent composite structures of the presentinvention comprise semi-continuous absorbent composites. Preferably,such structures are formed from non-continuous absorbent structuresdescribed herein. Such semi-continuous absorbent structures aredisclosed and claimed in co-pending, commonly-assigned U.S. patentapplication Ser. No. 08/142,259, filed (Oct. 22, 1993), Attorney DocketNo. JA-67U .

A preferred embodiment of a semi-continuous absorbent composite is shownin FIG. 10 as composite 90 comprising a non-continuous porous absorbentmacrostructure layer 91 and a continuous substrate layer 92. Thesubstrate layer is a double-ply of a Bounty®-type sheet that ischemically bonded to the absorbent macrostructure layer by Kymene®.Absorbent composite 90 shown in FIG. 10 has an absorbent macrostructurelayer 91 having a net-like shape. Semi-continuous absorbent composites90 can also comprise absorbent elements or strands 91 of porousabsorbent macrostructures bonded to substrate layer 92 by Kymene® asshown in FIGS. 11 and 12.

DETAILED DESCRIPTION OF METHODS FOR MAKING ABSORBENT COMPOSITES OF THEINVENTION

A. Method for Making Continuous Absorbent Composites

A method for making a continuous absorbent composite of the presentinvention can comprise the step of attaching, preferably bonding, atleast one continuous absorbent macrostructure, preferably in the form ofa sheet, to at least one substrate.

(1) Method of Making Absorbent Macrostructure Layers

Methods for making continuous absorbent macrostructure layers fromsubstantially water-insoluble, absorbent hydrogel-forming polymerparticles are disclosed in co-pending, commonly-assigned U.S.application Ser. No. 955,638, to Michael S. Kolodesh et al, entitled"Method and Apparatus for Making Cohesive Sheets from ParticulateAbsorbent Polymeric Composition," filed Oct. 2, 1992, the disclosure ofwhich is incorporated by reference. Absorbent macrostructure layers madethereby can then be attached to one or more substrate, or distributingmeans, or support means, to form the continuous absorbent compositestructures.

In a method for making an absorbent macrostructure layer of the presentinvention, the absorbent precursor particles are treated with ansufficient amount of the crosslinking agent to react with the polymermaterial at the surface of the particles so as to cause effectivecrosslinking, i.e., the crosslinked surface of the particle swells lessin the presence of aqueous body fluids relative to the uncrosslinkedportions. Preferably, the crosslinking agent is a cationicamino-epichlorohydrin adduct. Optionally, units of absorbentmacrostructures made separately (e.g. one unit comprises 4-10 absorbentprecursor particles), preferably by a crosslinking agent or aninterconnecting means for the unit macrostructure can be mixed with theabsorbent precursor particles. What constitutes "a sufficient amount" ofthe crosslinking agent depends upon a number of factors, including theparticular absorbent precursor particles treated, the particularcrosslinking agent used, the particular effects desired in forming theinterparticle bonded aggregate, and like factors. In the case ofmonomeric amino-epichlorohydrin adducts, such as apiperazine-epichlorohydrin adducts, the amount of adduct used can be inthe range of from about 0.1 to about 3 parts by weight, preferably fromabout 0.5 to about 1.5 parts by weight, most preferably from about 0.8to about 1.2 parts by weight, per 100 parts by weight of the absorbentprecursor particles. In the case of preferred polymericamino-epichlorohydrin resins, such as Kymene® 557H, 557LX or Plus, theamount of resin used can be from about 0.1 to about 5 parts by weight,preferably from about 0.5 to about 2.5 parts by weight, most preferablyfrom about 1 to about 2 parts by weight, per 100 parts by weight of theabsorbent precursor particles.

Besides the absorbent precursor particles and the crosslinking agent,other components or agents can be used as aids in preparing theinterparticle bonded aggregates. For example, water is typically usedwith the adduct to form an aqueous treatment solution thereof. Waterpromotes the uniform dispersion of the adduct on the surface of theprecursor particles and causes permeation of the crosslinking agent intothe surface regions of these particles. Water also promotes a strongerphysical association between the treated precursor particles, providinggreater integrity of the resultant interparticle bonded crosslinkedaggregates. In the present invention, water is used in an amount of lessthan about 25 parts by weight (i.e. from 0 to about 25 parts by weight),preferably in the range of from about 3 to about 15 parts by weight,more preferably in the range of from about 5 to about 10 parts byweight, per 100 parts by weight of the precursor particles. The actualamount of water used can vary depending upon the type of crosslinkingagent used, the type of polymer material used in forming the precursorparticles, the particle size of these precursor particles, the inclusionof other optional components (e.g., glycerol) and like factors.

Organic solvents can be used, usually to promote uniform dispersion ofthe crosslinking agent onto the surface of the precursor particles.These organic solvents are typically hydrophilic, and can include loweralcohols such as methanol and ethanol; amides such asN,N-dimethylformamide and N,N-diethylformamide; and sulfoxides such asdimethylsulfoxide. If a hydrophilic solvent is used, it is in an amountof less than about 20 parts by weight (i.e. from 0 to about 20 parts byweight), preferably in the range of from about 5 to about 15 parts byweight, more preferably in the range of from about 8 to about 12 partsby weight, per 100 parts by weight of the precursor particles. Theactual amount of hydrophilic solvent used can vary depending upon thecrosslinking agent used, the polymer material used forming the precursorparticles, the particle size of these precursor particles and likefactors.

As previously noted, the use of hydrophilic organic solvents is notnecessarily required in preparing bonded particle aggregates of thepresent invention. Indeed, it can be desirable to avoid the use of suchorganic solvents. Such solvents typically need to be removed from theaggregate before it is suitable for its intended use. The removal oforganic solvents is frequently an energy and process intensive, and addsadditional processing costs. Some hydrophilic solvents, such asisopropyl alcohol or t-butyl alcohol, can cause theamino-epichlorohydrin adduct to, precipitate out of solution and aretherefore undesirable for this reason. Indeed, the only solventstypically used in preparing the bonded particle aggregates of thepresent invention are the lower alcohols such as methanol and ethanolthat are not too energy or process intensive to remove, and do not causethe crosslinking agent, specifically an amino-epichlorohydrin adduct, toprecipitate out of aqueous solution.

Other optional components can also be used with the crosslinking agent,and especially aqueous treatment solutions thereof. It is particularlypreferred that the treatment solution comprising the crosslinking agentinclude a plasticizer, especially when the crosslinking agent is acationic amino-epichlorohydrin adduct and the treated precursorparticles are ambient temperature cured as described hereafter. In theabsence of a plasticizer, the treated precursor particles, when formedinto the interparticle bonded aggregates, can be relatively brittle, andthus more difficult to handle, especially in making the ultimatelydesired absorbent structures. Inclusion of a plasticizer in thetreatment solution insures that the resulting interparticle bondedaggregates (when ambient temperature cured) form relatively flexibleporous, absorbent macrostructures, particularly flexible, porous,absorbent sheets of the interparticle bonded aggregates. These flexiblesheets are relatively easy to handle in making the ultimately desiredabsorbent structures.

Suitable plasticizers include glycerol or water, alone or in combinationwith other components such as glycerol, propylene glycol (i.e.1,2-propanediol), 1,3-propanediol, ethylene glycol, sorbitol, sucrose,polymeric solutions such as those involving polyvinyl alcohol, esterprecursors of polyvinyl alcohol, or polyethylene glycol, or mixturesthereof. These other components in the plasticizer, such as glycerol,are believed to act as humectants, coplasticizers or both, with waterbeing the primary plasticizer. The preferred plasticizer for use in thepresent invention is a mixture of glycerol and water, particularly whenincluded as part of an aqueous treatment solution of an cationicaminoepichlorohydrin adduct, in a weight ratio of glycerol to water offrom about 0.5:1 to about 2:1, preferably from about 0.8:1 to about1.7:1.

The actual amount of plasticizer used can vary depending upon theparticular plasticizer used, the type of polymer material used informing the precursor particles, the type and amount of crosslinkingagent, and the particular flexibility effects desired from theplasticizer. Typically, the plasticizer is used in an amount of fromabout 5 to about 100 parts by weight, preferably from about 5 to about60 parts by weight, more preferably from about 10 to about 30 parts byweight, most preferably from about 15 to about 20 parts by weight, per100 parts by weight of the precursor particles.

The absorbent precursor particles can be treated with the crosslinkingagent, and most preferably with a cationic amino-epichlorohydrin adduct,typically an aqueous solution thereof, by any of a variety oftechniques. These include any method for applying solutions tomaterials, including coating, dumping, pouring, dropping, spraying,atomizing, condensing, or immersing the absorbent precursor particleswith the cationic amino-epichlorohydrin adduct, or solution thereof. Asused herein, the term "applied" means that at least a portion of thesurface area of at least some of the precursor particles to be bondedtogether has an effective amount of the adduct on it to cause surfacecrosslinking. In other words, the cationic adduct can be applied ontosome of the precursor particles, all of the precursor particles, aportion of the surface of some or all of the precursor particles, or theentire surface of some or all of the precursor particles. Preferably,the adduct is coated onto the entire surface of most, preferably all, ofthe absorbent precursor particles so as to enhance the efficiency,strength, and density of the interparticle bonds between the precursorparticles, as well as the desired surface crosslinking of the polymermaterial in the surface of these precursor particles.

After the treatment solution has been applied onto the precursorparticles, the treated precursor particles are mixed or layered togetherby any of a number of mixing or layering techniques to insure that theprecursor particles are thoroughly coated with the treatment solution.Because the precursor particles are thoroughly coated with the treatmentsolution, the efficiency, strength, and density of the bonds between theprecursor particles is enhanced, as well as surface crosslinkingresulting from the reaction of the cationic adduct with the polymermaterial forming the precursor particles. This mixing can beaccomplished using various techniques and apparatus, including variousmixers or kneaders, as are known in the art.

After the treatment solution has been applied to the precursorparticles, the treated precursor particles are physically associatedtogether to form an aggregate macrostructure. The term "physicallyassociated" is used herein to mean that the precursor particles arebrought together and remain in contact with each other as componentparts in any of a number of various ways and spatial relationships so asto form a single unit (an aggregate macrostructure).

The precursor particles are preferably physically associated together byapplying an associating agent onto the precursor particles andphysically contacting the precursor particles at least the portion ofthe surface of the precursor particles having the associating agentapplied thereto. Preferred associating agents cause the polymer materialof the precursor particles, when brought together, to adhere together bythe action of fluid surface tension forces and/or the entanglement ofpolymer chains due to external swelling. Associating agents useful inthe present invention include hydrophilic organic solvents, typicallylow molecular weight alcohols such as methanol or ethanol; water; amixture of hydrophilic organic solvents and water; the cationicamino-epichlorohydrin adducts previously described, or mixtures thereof.Preferred associating agents are water, methanol, ethanol, crosslinkingagent, most preferably a cationic polymeric amino-epichlorohydrin resinssuch as Kymene200 557H, or 557LX or Plus, or mixtures thereof. Typicallythe associating agent comprises a mixture including a cationicamino-epichlorohydrin adduct such that the step of applying the adductis carried out simultaneously with the step of applying the associatingagent.

The associating agents can be applied to the precursor particles by anyof various techniques and apparatus used for applying solutions tomaterials including coating, dumping, pouring, spraying, atomizing,condensing, or immersing the associating agent on the precursorparticles. The associating agent is applied to at least a portion of thesurface of at least some of the precursor particles to be bondedtogether. Preferably, the associating agent is coated onto the entiresurface of most, preferably all, of the precursor particles. Theassociating agent is generally mixed with, or sprayed onto, theprecursor particles by any of a number of mixing/spraying techniques andmixing/spraying apparatus to insure that the precursor particles arethoroughly coated with the associating agent.

When an associating agent has been applied to the precursor particles,the precursor particles can be physically contacted together in a numberof different ways. For example, the associating agent alone can hold theparticles together in contact. Alternatively, gravitational forces canbe used to insure contact between the precursor particles, e.g., bylayering precursor particles. Further, the particles can be placed in acontainer having a fixed volume so as to insure contact between theprecursor particles.

The precursor particles can alternatively be physically associatedtogether by physically constraining the precursor particles such thatthey are in contact with each other. For example, the precursorparticles can be packed tightly into a container having a fixed volumesuch that the precursor particles physically contact each other.Alternatively or in combination with the above procedure, gravitationalforces (e.g., layering) can be used to physically associate theprecursor particles. The precursor particles can also be physicallyassociated together by electrostatic attraction or by the introductionof an adhering agent (e.g., an adhesive material such as a water-solubleadhesive) to adhere them together. The precursor particles can also beattached to a third member (a substrate) such that the precursorparticles are brought into contact with each other by the substrate.

In an example of the method of the present invention, the aggregatemacrostructure can be shaped into various geometries, spatialrelationships, and densities to form an aggregate having a definedshape, size, and/or density. The aggregate can be shaped by anyconventional shaping techniques as are known in the art. Preferredmethods for shaping the aggregate include casting, molding, or formingoperations. Casting and molding techniques generally involve introducingthe precursor particles into a prepared mold cavity and applyingpressure to (compressing) the aggregate to cause the aggregate toconform to the shape of the mold cavity. Examples of specific moldingtechniques for use herein include compression molding, injectionmolding, extrusion or laminating. For example, a multiplicity ofprecursor particles can be added to a container having a fixed volumemold cavity and the aggregate compressed to conform to the shape of themold cavity so that the resultant macrostructure has the same shape.Forming techniques involve performing various operations on theaggregate to modify its shape, and/or size, and/or density. Examples ofspecific forming techniques for use herein include rolling, forging,extruding, spinning, coating or drawing operations. For example, anaggregate mixture of the precursor particles and at least the cationicamino-epichlorohydrin adduct can be passed between a pair of compactionrolls to form an aggregate sheet. Alternatively, the aggregate mixturecan be extruded through an orifice to form an aggregate having a shapecorresponding to that of the orifice. Further, the aggregate mixture canbe cast on a surface to form an aggregate having a desired shape orsurface morphology. Any or all of these techniques can also be used incombination to form the shaped aggregate. Any suitable apparatus as areknown in the art can be used to carry out such operations, which can beperformed with the material or portions of the apparatus either hotand/or cold.

In forming the aggregate macrostructure layers into particular shapes,and especially sheets, the density should be carefully controlled,particularly during the compaction step described above. If the densityof the shape aggregate macrostructure is too high, it can be more proneto gel blocking. Conversely, if the density is too low, the absorbencyof shaped aggregate macrostructure can be reduced. Shaped aggregatemacrostructure layers of absorbent composites of the present inventionusually have a density of from about 0.7 to about 1.3 g/cc, preferablyfrom about 0.8 to about 1.1 g/cc, and most preferably from about 0.9 toabout 1.0 g/cc.

In an example of the method of the present invention, an aggregatemixture of precursor particles, a cationic amino-epichlorohydrin adduct,water, humectant/co-plasticizer (optional), and a hydrophilic organicsolvent are added to the hopper of a conventional extruder apparatus.Such an extruder apparatus is shown in FIG. 12-14 of Principles ofPolymer Materials, Second Edition, (McGraw Hill Book Company, 1982) atpage 331, which publication is incorporated reference. The aggregatemixture is extruded through the orifice of the extruder apparatus tofeed a pair of driven compaction rolls having a fixed (but variable) gapbetween the rolls so as to compress the aggregate into the form of asheet. The sheet is then processed to specific lengths to providemacrostructure layers that have a specifically designed size, shapeand/or density.

(2) Continuous Method of Making Absorbent Macrostructure Layer

A preferred continuous method for making absorbent macrostructure sheetscan best be understood by reference to FIG. 19 which shows apparatus 301for carrying it out. Apparatus 301 has frame 302 for supporting itsvarious components. Apparatus 301 comprises a support means, shown inFIG. 19 as moving conveyor 303 which moves in the direction of arrow310. Feeders 305a through 305e supply a predetermined amount ofprecursor particles onto the conveyor. Optionally, the precursorparticles can contain units of absorbent macrostructures made separately(e.g. one unit comprises 4-10 absorbent precursor particles), preferablyby a crosslinking agent or an interconnecting means for the unitmacrostructure, whereby feeders 305a through 305e can supply a mixtureof the absorbent precursor particles and the units of absorbentmacrostructure. Conveyor 303 first passes under an initial sprayer 304a.After passing under initial sprayer 304a, conveyor 303 passes under atleast one means for continuously layering a predetermined amount of theprecursor particles or the mixture onto the conveyor. This is shown inFIG. 19 as feeders 305a through 305e. Conveyor 303 also passes under atleast one means for spraying a predetermined amount of treatmentsolution onto the layer of precursor particles on the conveyor. This isshown in FIG. 19 as sprayers 304b through 304f. Apparatus 301 furthercomprises a pair of non-planar opposing pressure applicators down streamfrom feeders 305 and sprayers 304. The pressure applicators are shown inFIG. 19 as a pair of compaction rolls 306. Also shown in FIG. 19 asbeing part of apparatus 301 is a slitting and transfer conveyor 307,knife and anvil rolls 308, and a sheet accumulator 309.

Conveyor 303 can be a flat belt conveyor that has good releaseproperties, such as polyurethane, which is commonly used in the foodindustry. The width of the conveyor is determined by the desired sheetsize. The conveyor generally moves in the direction of arrow 310 frompoint 311, where the initial sprayer 304a is located, to a point 312,where the knife and anvil rolls 308 are located. Conveyor 303 wouldtypically be an endless conveyor as shown in FIG. 19.

Conveyor 303 first passes under an initial sprayer 304a, where theconveyor is sprayed with a predetermined amount of treatment solution soas to cover a predetermined area of the conveyor. This initial sprayinginsures that the bottom part of the first precursor particle layer isexposed to the treatment solution. Also, the wet conveyor surface willprevent the subsequently fed particles from bouncing away from theirdesired placement. However, the initial spraying step is not absolutelynecessary, especially when the first layer of particles to be placed onthe conveyor is relatively thin, or when the conveyor travels at slowerspeeds.

Sprayer 304a (as well as sprayers 304b through 304f) must deliver asubstantially uniform mist, atomized spray and should have a low impactforce to avoid possible blow off of precursor particles. One sprayerthat has been found to work well is a model 6218-1/4 JAU atomized airactuated nozzle assembly, available from Spraying Systems Co., Wheaton,Ill. 60188. Conveyor 303 then passes under feeder 305a where apredetermined amount of dry precursor particles is layered onto thepredetermined area of the conveyor. The amount of precursor particles tobe layered onto conveyor 303 depends on a number of factors including,but not limited to, the desired density of the resultant sheet, thenumber of layering steps to be performed, the size of the particlesbeing used and the desired width of the resultant sheet. At a minimumthe predetermined amount should be enough to substantially cover apredetermined area of the conveyor with a layer one particle inthickness.

Feeder 305a (as well as feeders 305b through 305e) must be capable ofdistributing the precursor particles in a thin and preferably widelayer. Thinner layers on the conveyor insure that all of the particlesare treated during subsequent spraying steps and wider layers willincrease production output. Vibrating feeders have been shown to beadequate for layering the dry precursor particles onto the conveyor. Anexample of a suitable vibrating feeder is a Super Feeder model#2106E-003S4, commercially available from Solids Flow Control, P.O. Box410767, 14201-A South Lakes Drive, Charlotte, N.C. 28241-0767. Thisfeeder has a weight feed-back control system for accuracy. Conveyor 303then passes under a second sprayer 304b. A predetermined area ofconveyor 303 having the first layer of precursor particles is sprayedwith a predetermined amount of the same treatment solution used ininitial sprayer 304a. In general, the predetermined amount of treatmentsolution is related to the amount of particles in the layer. The greaterthe amount of particles in the layer, the more treatment solution isneeded to treat substantially all of the particles.

The metering and spraying steps can then be repeated a number of times(e.g., using feeders 305b through 305e and sprayers 304c through 304f)depending on the desired density of the ultimate sheet. When themetering and spraying steps are repeated a number of times and theinitial spraying step is performed, as described above, the first layerof particles is exposed to two spray applications. Therefore, theinitial spraying step and the first post-layering spraying step eachneed only spray half the amount of treatment solution needed to treatthat amount of particles in the first layer on conveyor 303. The othersprayers 304c through 304f will spray the normal amount of treatmentsolution, i.e. twice the amount of either the initial or firstpost-laying spray.

After all of the layering and spraying steps have been performed, thetreated precursor particles typically loosely adhere together to form aweb. Conveyor 303 then moves this web and delivers it to a pair ofopposing pressure applicators. The pressure applicators shown in FIG. 19take the form of compaction rolls 306. However, as will be appreciatedto those skilled in the art, an intermittent conveyor method could beused, with opposing plates or platens used to compress the web.

Compaction rolls 306 can have a non-planar, rough surface. As the webpasses through compaction rolls 306, the pressure on the web causes itto expand. The rough surface of rolls 306 reduces the sliding effectbetween the rolls and the web in contact with the rolls. This in turnreduces expansion of the web in both the machine direction 310 andcross-machine direction. Machine direction expansion is undesirablebecause it requires compaction rolls 306 to speed up in order to matchthe machine direction expansion. Compaction by rolls 306 densities theweb of freely deposited layers of precursor particles and sprayedtreatment solution into a sheet.

Compaction rolls 306 can be in the form of cylindrical stainless steelrolls that are coated with a plasma coating, thereby giving the rolls arough surface and causing them to release the web more easily aftercompaction. Examples of suitable coatings include coating #'s 934 and936, available from Plasma Coatings, Inc., Waterbury, Conn. 06702. Thegap between the compaction rolls determines the amount of compactionapplied to the web.

Apparatus 301 can include a slitter to trim the web edges prior tocompaction. The edges of the web can have a less uniform density thanthe rest of the web, and are typically subjected to inconsistentapplication of treatment solution and particles due to the conveyor beltmovement in the cross-machine direction, thus making removal desirable.The slitter can be a regular circular knife working against a hardsurface such as a transfer conveyor belt, as indicated by 307.

After the web passes through compaction rolls 306, a sheet is formed andcollected in accumulator 309. Accumulator 309 can take the form of awind-up roll that rolls up the sheet into a single roll of a desiredsize. When the desired size roll is obtained apparatus 301 can have asecond slitter to cut the sheet. This second slitter can take the formof knife and anvil roll 308.

(3) Method of Making Absorbent Composites from Absorbent MacrostructureLayers

Starting with one or more continuous absorbent macrostructure layers asdescribed above, an absorbent composite structure can be made byattaching thereto one or more substrates. Attachment of the substrate tothe absorbent macrostructure layer is made by a substrate attachingmeans. In preferred embodiments, the substrate material comprises acellulosic material or a material having cellulosic functionality on atleast the surface. In these embodiments, the substrate attaching meanspreferably comprises a bonding treatment by a crosslinking agent that iscapable of crosslinking the absorbent polymer molecules of the absorbentgelling particles. More preferably, the bonding treatment is by acationic amino-epichlorohydrin adduct, more preferably Kymene®.

The layers of absorbent macrostructures and substrates can be broughttogether by methods well known in the art. In a preferred method, acontinuous sheet layer of absorbent macrostructure is supplied, and isbrought into contact and registered with a substrate layer. Apredetermined amount of an attachment means, preferably in liquid form,is applied continuously to the surface of either the absorbentmacrostructure layer or the substrate layer, or both, prior toregistering of the layers. One or more additional substrates orabsorbent macrostructure layers can be further applied to the composite.The resulting composite is preferably compacted and cured in accordancewith the methods described herein. The result is a continuous sheet ofan absorbent composite having a layered structure as herein described.

As previously noted, the steps in the method of the present inventionfor producing an absorbent macrostructure, or for forming an absorbentmacrostructure layer, need not be carried out in any specific order, andcan be carried out simultaneously. For example, the crosslinking agentcan be applied simultaneously with the physical association of theprecursor particles, shaped into a preferred shape and typically adesired density, and then the adduct reacted with the polymer materialof the precursor particles, either immediately after the above steps arecompleted or after the aggregate has been left standing for a period oftime, to simultaneously surface crosslink the precursor particles andform the aggregate macrostructure. Typically, the precursor particlesare mixed or sprayed with a solution of the adduct, water, a humectantand/or coplasticizer (e.g., glycerol), and a hydrophilic organic solvent(e.g., methanol) to form an adhered together aggregate. Optionally, theabsorbent precursor particles can contain units of absorbentmacrostructures made separately (e.g. one unit comprises 4-10 absorbentprecursor particles), preferably by a crosslinking agent or aninterconnecting means for the unit macrostructure. The adduct, water,humectant/coplasticizer and hydrophilic organic solvent serve as theassociating agent for the precursor particles, the adduct also servingas the crosslinking agent. The adhered aggregate (i.e. the associatedprecursor particles and the aqueous mixture) is subsequently shaped intoa densified sheet by a combination of extruding and rolling techniquesas described above. The adduct is subsequently reacted with the polymermaterial by ambient or heat curing to simultaneously cause crosslinkingat the surface of the precursor particles and to form a cohesiveinterparticle bonded aggregate macrostructure.

Under certain conditions, especially if the treated precursor particleshave been heat cured, the resultant macrostructures can be somewhatinflexible and potentially brittle. In such cases, the macrostructurescan be made more flexible by treating it with a plasticizer. Suitableplasticizers include water, alone or in combination with thehumectants/coplasticizers previously described, preferably glycerol. Theplasticizer can be applied to the macrostructures in a number ofdifferent ways, including spraying, coating, atomizing, immersing, ordumping the plasticizer onto the macrostructure. Alternatively, in thecase of water alone, the macrostructure can be placed in a high humidityenvironment (e.g., greater than 70% relative humidity). The amount ofplasticizer applied to the macrostructure can be selected depending uponthe specific plasticizer used, and the effects desired. Typically, theamount of plasticizer applied is from about 5 to about 100 parts byweight, preferably from about 5 to about 60 parts by weight, per 100parts by weight of the macrostructure. A particularly preferredplasticizer comprises a mixture of glycerol and water in a weight ratioof from about 0.5:1 to about 2:1, preferably from about 0.8:1 to about1.7:1. As shown in FIGS. 13 through 16 and especially FIGS. 15 and 16,the macrostructures resulting from the method of the present inventionhave pores (the dark areas of the photomicrograph) between adjacentprecursor particles. The pores are small interstices between adjacentprecursor particles that allow the passage of liquid into the interiorof the macrostructure. The pores are formed into the macrostructurebecause the precursor particles do not "fit" or pack tightly enough,even when compressed, to eliminate the pores. (The packing efficiency ofthe precursor particles is less than 1.) The pores are generally smallerthan the constituent precursor particles and provide capillaries betweenthe precursor particles to transport liquid into the interior of themacrostructure.

Various types of fiber material can be used as the reinforcing membersin the macrostructure layers of the present invention, or asco-absorbent material. Any type of fiber material which is suitable foruse in conventional absorbent products is also suitable for use in themacrostructures herein, including fiber material previously described.The fiber material can be added to the macrostructure layers byintroducing the fibers into treatment solution containing thecrosslinking agent, by mixing with the precursor particles prior toapplying the crosslinking agent, or by adding the fiber material to thecrosslinking agent/precursor particle mixture. For example, the fibermaterial can be kneaded into the crosslinking agent/precursor particlemixture. The fiber material is preferably thoroughly mixed with thesolution so that the fiber material is uniformly dispersed throughoutthe macrostructure. The fibers are also preferably added before reactingthe crosslinking agent with the polymer material of the precursorparticles.

(4) Continuous Method Of Making Absorbent Composites

A preferred continuous method for making a continuous absorbentcomposite comprises a step of introducing at least one substrate memberinto a continuous method described, herein above and illustrated in FIG.19 for making a continuous absorbent macrostructure. In this method, asubstrate comprising a first and a second surface is supplied, and afirst amount of a substrate attaching means for attaching the substrateto an absorbent macrostructure layer is applied to a first area of thefirst surface of the substrate. Preferably, the substrate is acellulosic material or a material that has cellulosic functionality onat least one surface thereof. The substrate attaching means preferablycomprises a chemical bonding agent which can bond to both the substrateand to the absorbent gelling particles of the macrostructure layer. Morepreferably, the bonding agent comprises a crosslinking agent for theabsorbent gelling polymer which can chemically bond to the substrate andto macrostructure layer. A highly preferred bonding agent comprises acationic amino-epichlorohydrin adduct, more preferably Kymene®.

In the next step, a first predetermined amount of absorbenthydrogel-forming polymer particles are applied as a first layer having athickness to the first area of the first surface of the substrate suchthat the particles become at least partially contacted with the amountof substrate attaching means, thereby forming a first layer of theabsorbent polymer particles. Optionally, the absorbent polymer particlescan contain units of absorbent macrostructures made separately (e.g. oneunit comprises 4-10 absorbent polymer particles), preferably by acrosslinking agent or an interconnecting means for the unitmacrostructure. In a preferred step, the particle layer is substantiallyuniform in thickness. When the substrate attaching means is a fluidmaterial, the gelling particles adhere to the substrate through thesubstrate attaching means. When the substrate attaching means cures orbecomes set, such as when an adhesive hardens or a chemical bondingagent has bonded, the gelling particles become more permanently attachedto the substrate. In a preferred step wherein the substrate attachingmeans comprises a crosslinking agent comprising a cationicamino-epichlorohydrin adduct, the first layer of gelling particlesbecome bonded to the substrate through the adduct upon curing of theadduct.

In a next step, a first amount of a crosslinking agent is applied to atleast a portion of the surfaces of the polymer particles of the firstlayer. Preferably, the crosslinking agent is a liquid and is appliedsubstantially uniformly to substantially the entire surface of theabsorbent gelling particles of the first layer. Preferably thecrosslinking agent comprises a cationic amino-epichlorohydrin adduct.Upon curing, the polymer material in the contacted surfaces of theparticles of the first layer become crosslinked, and the portions of thesurface of the gelling particles become interconnected to at least oneadjacent particle, thereby forming a porous, absorbent macrostructure asherein described.

In a preferred method, additional layers of absorbent gelling particles(optionally including the units of absorbent macrostructure) are addedin successive layers. Such method therefore comprises the step ofapplying a second predetermined amount of absorbent gelling particles tothe first layer of absorbent particles, thereby forming a second layerof absorbent gelling particles. The absorbent gelling particles of thesecond layer become at least partially contacted with and adhere to thefirst particle layer through the first amount of crosslinking agent.Additional crosslinking agent is applied to the surface of the absorbentgelling particles of the second (and successive) layer substantially asdescribed for the first layer. Upon curing, the polymer material in thecontacted surfaces of the particles of the second (and successive) layerbecome crosslinked, and the portions of the surface of the gellingparticles become interconnected to at least one adjacent particle,thereby forming a porous, absorbent macrostructure as herein described.

A method of making a continuous composite can further comprise the stepof attaching or bonding at least one layer of absorbent particles ontothe second surface of the substrate. Such method comprises the step ofapplying to a third area of the second surface of the substrate a secondamount of a substrate attaching means for attaching the second surfaceof the substrate to an absorbent macrostructure layer. A thirdpredetermined amount of the absorbent gelling particles (optionallyincluding the units of absorbent macrostructure) is applied in a layerto the third area, such that the particles become at least partiallycontacted with the third amount of substrate attaching means, therebyforming a layer of the absorbent polymer particles on the second surfaceof the substrate. As described herein above, a third amount of acrosslinking means comprising a crosslinking agent is applied to atleast a portion of the surfaces of the polymer particles of the thirdlayer, which, upon curing, forms a porous, absorbent macrostructure.Additional layers of absorbent gelling particles can also besuccessively added to the layer of absorbent gelling particles on thesecond surface of the substrate.

A preferred method of making continuous composite structures comprisesthe further step of attaching at least a second substrate layer onto thesurface of the absorbent macrostructure layer of the composite. Themethod comprises the step of applying to a predetermined first surfacearea of a second (or successive) substrate a third amount of a substrateattaching means for attaching the first surface of the second substrateto an absorbent macrostructure layer. This step can be accomplishedsubstantially as described above for attaching absorbent particle layersto the first substrate. The first surface of the second substrate canthen be registered with and attached to a surface of an absorbentmacrostructure layer. The substrate attaching means, preferably inliquid form, contacts with and adheres to portions of the gellingparticles at the surface of the absorbent macrostructure layer. When thesubstrate attaching means cures or becomes set, such as when an adhesivehardens or a chemical bonding agent has bonded, the gelling particles atthe surface of the macrostructure become more permanently attached tothe second substrate. In a preferred step wherein the second substrateis a cellulosic substrate, or has cellulosic functionality at least atthe surface, and substrate attaching means comprises a crosslinkingagent comprising a cationic amino-epichlorohydrin adduct, the absorbentmacrostructure layer becomes bonded to the substrate through the adductupon curing of the adduct. In an alternative step, the third amount ofsubstrate attaching means can be applied to the surface of the absorbentmacrostructure layer, prior to registering with and attaching the firstsurface of the second substrate thereto.

A method for making a continuous composite structure of the presentinvention can further comprise the steps of adding successive layers ofabsorbent particles (optionally including the units of absorbentmacrostructure) and substrates, in combination with the other stepsdescribed above, to form a variety of layered absorbent compositestructures as herein before described.

Preferably, in combination with any of the above steps, the resultinglayered composite is compacted or pressed together to improve thecontact, and interconnection, of the absorbent gelling particles withadjacent particles and with the substrate layers. A preferred methodcomprises the step of continuously passing the layered composite throughopposing pressure means, more preferably between a pair of opposingpressure rollers, thereby continuously forming a continuous absorbentcomposite.

In a preferred method for making an absorbent composite of the presentinvention employs a continuous means of supplying a substrate layer andan absorbent macrostructure layer material, or components thereof. Apreferred continuous method for making an absorbent composite can bestbe understood by reference to FIG. 19 which shows apparatus 301 forcarrying it out. Apparatus 301 has frame 302 for supporting its variouscomponents. Apparatus 301 comprises moving conveyor 303 which moves inthe direction of arrow 310. Feeders 305a through 305e supply apredetermined amount of precursor particles onto the conveyor.Optionally, the precursor particles can contain units of absorbentmacrostructures made separately e.g. one unit comprises 4-10 absorbentprecursor particles), preferably by a crosslinking agent or aninterconnecting means for the unit macrostructure, whereby feeders 305athrough 305e can supply a mixture of the absorbent precursor particlesand the units of absorbent macrostructure. Apparatus 301 furthercomprises sheet feeder 313 for supplying a substrate 314. Sheet feeder313 includes a wind-up roll that rolls up the substrate 314 having adesired size. The width of the Bounty sheet 314 is smaller than that ofmoving conveyor 303. In operation, sheet feeder 313 feeds the rolledsubstrate 314 to moving conveyor 303. The Bounty sheet 314 on conveyor303 first passes under an initial sprayer 304a, where the substrate issprayed with a predetermined amount of treatment solution so as to covera predetermined area of the substrate. After passing under initialsprayer 304a, conveyor 303 passes under at least one means forcontinuously layering a predetermined amount of precursor particles ontothe substrate 314. This is shown in FIG. 19 as feeders 305a through305e. Conveyor 303 also passes under at least one additional means forspraying a predetermined amount of treatment solution onto the layer ofprecursor particles on the substrate 314. This is shown in FIG. 19 assprayers 304b through 304f. Apparatus 301 further comprises a pair ofnon-planar opposing pressure applicators down stream from feeders 305and sprayers 304. The pressure applicators are shown in FIG. 19 as apair of compaction rolls 306. Also shown in FIG. 19 as being part ofapparatus 301 is a slitting and transfer conveyor 307, knife and anvilrolls 308, and a sheet accumulator 309.

Conveyor 303 can be a flat belt conveyor that has good releaseproperties, such as polyurethane, which is commonly used in the foodindustry. The width of the conveyor is determined by the desiredcomposite size. The conveyor generally moves in the direction of arrow310 from point 311, where the initial sprayer 304a is located, to apoint 312, where the knife and anvil rolls 308 are located. Conveyor 303would typically be an endless conveyor as shown in FIG. 19.

Conveyor 303 first passes under an initial sprayer 304a, where thesubstrate is sprayed with a predetermined amount of treatment solutionso as to cover a predetermined area of the substrate. This initialspraying insures that the bottom part of a first precursor particlelayer is exposed to the treatment solution. Sprayer 304a (as well assprayers 304b through 304f) must deliver a substantially uniform mist,atomized spray and should have a low impact force to avoid possible blowoff of precursor particles. One sprayer that has been found to work wellis a model 6218-1/4 JAU atomized air actuated nozzle assembly, availablefrom Spraying Systems Co., Wheaton, Ill. 60188. Conveyor 303 then passesunder feeder 305a where a predetermined amount of dry precursorparticles is layered onto the predetermined area of the substrate 314.The amount of precursor particles to be layered depends on a number offactors including, but not limited to, the desired density of theresultant sheet, the number of layering steps to be performed and thesize of the particles being used. At a minimum the predetermined amountshould be enough to substantially cover a predetermined area of thesubstrate with a layer one particle in thickness.

Feeder 305a (as well as feeders 305b through 305e) must be capable ofdistributing the precursor particles in a thin and preferably widelayer. Thinner layers on the substrate 314 insure that all of theparticles are treated during subsequent spraying steps and wider layerswill increase production output. Vibrating feeders have been shown to beadequate for layering the dry precursor particles onto the substrate314. An example of a suitable vibrating feeder is a Super Feeder model#2106E-003S4, commercially available from Solids Flow Control, P.O. Box410767, 14201-A South Lakes Drive, Charlotte, N.C. 28241-0767. Thisfeeder has a weight feed-back control system for accuracy.

Conveyor 303 then passes under a second sprayer 304b. A predeterminedarea of substrate 314 having the first layer of precursor particles issprayed with a predetermined amount of the same treatment solution usedin initial sprayer 304a. In general, the predetermined amount oftreatment solution is related to the amount of particles in the layer.The greater the amount of particles in the layer, the more treatmentsolution is needed to treat substantially all of the particles.

The metering and spraying steps can then be repeated a number of times(e.g., using feeders 305b through 305e and sprayers 304c through 304f)depending on the desired density of the absorbent macrostructure layer.When the metering and spraying steps are repeated a number of times andthe initial spraying step is performed, as described above, the firstlayer of particles is exposed to two spray applications. Therefore, theinitial spraying step and the first post-layering spraying step eachneed only spray half the amount of treatment solution needed to treatthat amount of particles in the first layer on substrate. The othersprayers 304c through 304f will spray the normal amount of treatmentsolution, i.e. twice the amount of either the initial or firstpost-laying spray.

After all of the layering and spraying steps have been performed, thetreated, precursor particles typically loosely adhere together to forman absorbent macrostructure layer on the substrate 314. Conveyor 303then moves this composite and delivers it to a pair of opposing pressureapplicators. The pressure applicators shown in FIG. 19 take the form ofcompaction rolls 306. However, as will be appreciated to those skilledin the art, an intermittent conveyor method could be used, with opposingplates or platens used to compress the composite.

Compaction rolls 306 can have a non-planar, rough surface. As thecomposite passes through compaction rolls 306, the pressure on thecomposite causes it to expand. The rough surface of rolls 306 reducesthe sliding effect between the rolls and the composite in contact withthe rolls. This in turn reduces expansion of the composite in both themachine direction 310 and cross-machine direction. Machine directionexpansion is undesirable because it requires compaction rolls 306 tospeed up in order to match the machine direction expansion. Compactionby rolls 306 densifies the sprayed treatment solution into the freelydeposited layers of precursor particles.

Compaction rolls 306 can be in the form of cylindrical stainless steelrolls that are coated with a plasma coating, thereby giving the rolls arough surface and causing them to release the composite more easilyafter compaction. Examples of suitable coatings include coating #'s 934and 936, available from Plasma Coatings, Inc., Waterbury, Conn. 06702.The gap between the compaction rolls determines the amount of compactionapplied to the composite.

Apparatus 301 can include a slitter to trim the web edges prior tocompaction. The edges of the composite can have a less uniform densitythan the rest of the composite, and are typically subjected toinconsistent application of treatment solution and particles due to theconveyor belt movement in the cross-machine direction, thus makingremoval desirable. The slitter can be a regular circular knife workingagainst a hard surface such as a transfer conveyor belt, as indicated by307.

After the web passes through compaction rolls 306, a continuouscomposite sheet is formed and collected in accumulator 309. Accumulator309 can take the form of a wind-up roll that rolls up the sheet into asingle roll of a desired size. When the desired size roll is obtainedapparatus 301 can have a second sillier to cut the sheet. This secondslitter can take the form of knife and anvil roll 308.

in the case where macrostructure layers are formed on both main surfacesof the substrate 314, a variety of methods can be employed. In onemethod, the same or similar process as the described above is carriedout on the second main surface of the substrate 314. More specifically,a continuous composite sheet comprising an absorbent macrostructurelayer and a substrate is stored on sheet feeder 314. Sheet feeder 314supplies the continuous composite sheet to the same, or a second,conveyor 303, this time with the absorbent macrostructure layer of thecomposite contacting the conveyer 303. Sprayer 304a through 304f andfeeder 305a through 305e operate as described above on the second mainsurface of the substrate 314, thereby forming a continuous compositesheet having macrostructure layers formed on each of the main surfacesof the substrate 314, e.g. as shown in FIG. 6.

In another method not shown in the Figures, a intermediate composite isprocessed as described above by applying one or more absorbent particlelayers to a first surface of a substrate. The intermediate composite isthen inverted so that the layers of absorbent particles on theintermediate composite are facing toward the conveyor 303. Theintermediate composite then passes as before under one or more sprayer304 and absorbent gelling particles addition means 305 to add one ormore additional layers of the gelling particles to the second mainsurface of the substrate. The composite can then be compacted, etc. aspreviously described.

Alternately, a first continuous absorbent macrostructure layer can bemade by applying one or more layers of absorbent gelling particles,followed by treatment solution, directly to the belt 303, then asubstrate layer can be introduced intermediate the conveying line 301 toregister and attach the first main surface of the substrate to the firstcontinuous absorbent macrostructure layer. Subsequently, a secondcontinuous absorbent macrostructure layer can be applied to the secondmain surface of the substrate by applying one or more layers ofabsorbent particles and treatment solution thereto.

Further, a composite can comprise a second substrate layer. Apredetermined area on the macrostructure layer, or a layer of gellingparticles applied from a feeder means 305, is sprayed with apredetermined amount of the same treatment solution used in initialsprayer 304a. A second substrate sheet can be brought into contact withthe sprayed macrostructure layer. As a result, a bonding between thesecond substrate sheet and the sprayed macrostructure layer can be madethrough crosslinking, whereby an absorbent composite having thestructure as shown in FIG. 2 can be obtained. Alternatively, apredetermined area of a second substrate sheet can be sprayed with apredetermined amount of the same treatment solution, and then applied tothe surface of an absorbent macrostructure.

Selectively repeating the above described steps about any continuousabsorbent composites, non-continuous absorbent composites having layeredstructures shown in FIGS. 3, 4 and 5 can be obtained.

Simultaneously or after the crosslinking agent has been applied, theprecursor particles have been physically associated together to form anaggregate, and the aggregate has been shaped, the crosslinking agent isreacted with the polymer material of the precursor particles, whilemaintaining the physical association of the precursor particles, toprovide effective surface crosslinking in the precursor particles in theaggregate macrostructure. The preferred crosslinking agent is cationicamino-epichlorohydrin adduct. Because of the relatively reactivecationic functional groups of the amino-epichlorohydrin adduct, thecrosslinking reaction between the adduct and the polymer material of theprecursor particles can occur at relatively low temperatures. Indeed,this crosslinking reaction (curing) can occur at ambient roomtemperatures. Such ambient temperature curing is particularly desirablewhen the treatment solution comprising the adduct additionally containsa plasticizer, such as a mixture of water and glycerol. Curing atsignificantly above ambient temperatures can cause the plasticizer to bedriven off due to its volatility, thus necessitating an additional stepto plasticize the resulting interparticle bonded aggregate. Such ambientcuring is typically carried out at a temperature of from about 18° C. toabout 35° C. for from about 12 to about 48 hours. Preferably, suchambient curing is carried out at a temperature of from about 18° C. toabout 25° C. for from about 24 to about 48 hours.

Although the crosslinking reaction between a cationicamino-epichlorohydrin adduct and the polymer material of the precursorparticles can occur at ambient temperatures, such curing can also becarried out at higher temperatures to speed up the reaction. Highertemperature curing typically involves heating the composite comprisingthe treated and associated precursor particles to cause the crosslinkingreaction between the adduct and the polymer material of the precursorparticles to occur in a shorter period of time, typically minutes. Thisheating step can be carried out using a number of conventional heatingdevices, including various ovens or dryers well known in the art.

Generally, heat curing can be carried out at a temperature above about50° C. for a period of time sufficient to complete the crosslinkingreaction between the adduct and the polymer material of the precursorparticles. The particular temperatures and times used in heat curingwill depend upon the particular cationic amino-epichlorohydrin adductused and the polymer material present in the precursor particles. If thecure temperature is too low, or the cure time too short, the reactionwill not be sufficiently driven, resulting in macrostructures that haveinsufficient integrity and poor absorbency. If the cure temperature istoo high, the structural integrity of the substrate means can bediminished. This can leave the absorbent composite with littleadditional dry or wet strength support from the substrate.

The crosslinking reaction between the cationic amino-epichlorohydrinadduct and the polymer material of the precursor particles issufficiently fast, even at ambient temperatures, such that it can becarried out in the absence of initiators and/or catalysts. However, animportant factor relative to the reactivity of the amino-epichlorohydrinadduct is the pH of the treatment solution containing the adduct.Typically, the pH of the treatment solution is from about 4 to about 9,preferably from about 4 to about 6. Maintenance of the treatmentsolution at a pH within these ranges insures that theaminoepichlorohydrin adduct will be sufficiently reactive, even atambient temperatures.

The physical association of the treated precursor particles needs to bemaintained during the curing step so that, as crosslinking occurs,adjacent precursor particles become cohesively bonded together, ifforces or stresses are sufficient to disassociate the precursorparticles that are present during the crosslinking reaction,insufficient bonding of the precursor particles can occur. This canresult in aggregates having poor structural integrity. The physicalassociation of the precursor particles is typically maintained byinsuring minimal dissociation forces or stresses are introduced duringthe curing step.

B. Method for Making Non-Continuous Absorbent Composites

A preferred method for making a non-continuous absorbent compositecomprises a first step of forming a plurality of slits or cutspenetrating at least partially, preferably completely, through thethickness of the continuous composite sheet. Preferably, at least asubstantial portion of, more preferably all of, said cuts are orientedin substantially the same direction in accordance with a predeterminedpattern. An example of a continuous composite in which a predeterminedpattern of cuts been made in a continuous, interlaced pattern is shownin FIG. 18. Voids are formed in the composite at the location of theslits when the slitted composite is then stretched in a directionsubstantially perpendicular to the direction of the slits, therebyforming the non-continuous composite. In general, the degree ofstretching of a slitted composite results in a larger void opening atthe site of the slit, and a larger percentage of void volume in theresulting non-continuous composite.

A preferred method for making a non-continuous absorbent compositecomprises a step of forming a slitted continuous absorbent composite 100as shown in FIG. 18. The step comprises forming intermittently, alongeach of a plurality of substantially parallel lines 101, a plurality ofslits 102 completely through the thickness of the composite. Thedistance 103 along a line between successive cuts 102 can be uniform,random, or ordered. Increasing the distance 103 between successive cutsin parallel lines decreases the percent void volume of thenon-continuous composite (after stretching) in that portion of thecomposite. Similarly, the spacing distance 105 between successiveparallel lines of slits can be uniformly the same, random, or ordered.Increasing the spacing distance 105 between successive parallel lines ofslits decreases the percent void volume of the non-continuous composite(after stretching) in the portion along the length of such parallellines.

in a preferred method, the slitted continuous absorbent composite 100 isstretched in the width direction 106 by from about 20% to about 400% ofthe width of the composite 100, whereby the average percent void volumeof from about 17% to about 80% can be obtained. More preferably, theslitted continuous absorbent composite 100 is stretched in the widthdirection 106 by from about 50% to about 300% of the width of thecomposite 100, whereby the average percent void volume of from about 33%to about 67% can be obtained.

A preferred method comprises making a non-continuous composites having afirst width area having a percent void area that is greater than that ofa second width area. In the first width area of this continuouscomposite, a series of substantially parallel lines of intermittent cutshaving a predetermined spacing 105 between adjacent lines is formed. Ina second width area adjacent to the first area, a second series ofsubstantially parallel lines of intermittent cuts having a widerpredetermined spacing 105 between adjacent lines is made, such that whenthe slitted composite 100 comprising both slitted areas is stretcheduniformly, the distance between adjacent voids formed by the slits inthe first width area of the composite is smaller than the distancebetween adjacent voids in the second area, and wherein the percentage ofvoid space in the first area of the non-continuous composite is greaterthan the percent void space in the second area.

In another preferred method, the spacing distance 105 between a seriesof successive lines in a first width area has the same spacing distance105 between a series of successive lines in a second width area.However, the distance or amount of stretching in the first width area ismade greater than the distance or amount of stretching in the secondarea. In the resulting non-continuous composite, the distance betweenvoids formed from the slits of the first width area of the composite isthe same as the distance between voids of the second width area.However, the area (width) of a void opening formed in the first widtharea is greater than the area (width) of a void opening in the secondwidth area, and subsequently the percent void space in the first widtharea of the non-continuous composite is greater than the percent voidspace in the second area.

Another preferred method involves making a non-continuous compositeshaving a first length area having a percent void area that is greaterthan that of a second length area. A series of substantially parallellines of intermittent cuts are made in a continuous composite. In afirst length area, successive intermittent cuts have a predetermined cutlength 102 and a predetermined spacing between successive cuts 103. In asecond length area, successive intermittent cuts have a shorter cutlength 102, but the same spacing 103 between successive cuts, comparedto the first length area. This slitted composite is then stretcheduniformly along both lengths. In the resulting non-continuous composite,the distance between adjacent voids formed from the slits of the firstlength area of the composite is substantially the same as the distancebetween adjacent voids of the second length. However, the area (length)of a void opening formed in the first length area is greater than thearea (length) of a void opening in the second length area, andsubsequently the percent void space in the first length area of thenon-continuous composite is greater than the percent void space in thesecond length area of the non-continuous composite.

In alternative methods, the lengths of cuts and spacing distance betweencuts of successive parallel lines of intermittent cuts can be varied toprovide, upon stretching of the slitted composite, non-continuouscomposites having voids of various shapes and sizes (areas), differentspacing between voids, and having different percent void areas. Thelengths of slits, the spacing distance between successive slits in aline, and the spacing between successive lines of slits can be varied toprovide non-continuous composites comprising areas having voids ofvarious shapes and sizes (areas), and having different percent voidspace in an area. The spaces and lengths can be selected to providedifferent absorbency and percentage void volume for a particularabsorbency requirement, or for a particular absorbent product. Thelength of the slit lines, the spacing between successive slits, and thespacing between successive parallel lines of slits can each also affectthe flexibility and extensity (how far the slitted sheet can bestretched). Of course, the thickness and density of the absorbentmacrostructure, the type of crosslinking agent used, the presence ofplasticizer in the macrostructure, the type of substrate material, andvarious other factors can also effect the flexibility of the slitted andstretched structure. However, for a given absorbent composite structure,in general, the flexibility of a structure, and the extensity of aslitted composite are inversely proportional to the spacing betweensuccessive parallel lines of slits.

The pattern of slits in the slitted composite can be made substantiallyuniform, randomly, or ordered. Typically, the length of slits is fromabout 2 mm to about 50 mm, preferably from about 5 mm to about 25 mm,more preferably about 10 mm to about 20 mm. Typically the spacingdistance between successive slits on a line is from about 1 mm to about20 mm, preferably from about 2 mm to about 10 mm, more preferably fromabout 3 mm to about 5 mm. Typically, the spacing between successiveparallel lines of slits is from about 1 mm to about 10 mm, preferablyfrom about 1.5 mm to about 5 mm, more preferably about 2 mm to about 3mm.

Another non-limiting example of slitting patterns which can be used isshown in FIG. 18A.

A preferred method of forming a slitted absorbent macrostructure, thatcan then be stretched to form voids at the location of the slits,involves continuously forming slits in a predetermined pattern. Thispreferred continuous method for making an absorbent composite can bestbe understood by reference to FIG. 20 which shows apparatus 401 forcutting machine-direction slits into a continuous composite. Apparatus401 comprises a continuous slit forming device 420. An unwinding roll402 supplies a continuous sheet 405 of continuous absorbent composite tothe slit forming device 420, and a wind-up roll 415 collects acontinuous sheet 412 of a slitted, partially stretched composite. Thecontinuous slit forming device 420 comprises a knife roll 422 with aplurality of knife blades 432, and a recess roll 424 having a pluralityof recess grooves 441 in the surface thereof. The continuous sheet ispassed through the opening 421 between the knife roll 422 and the recessroll 424. The knife roll 422 and the recess roll 424 are rotated inopposite directions about their respective axes 423 and 426. Both theknife roll and the recess roll are each adjustable in their relativevertical and horizontal pitch and axial alignment. The absorbentcomposite is essentially pulled through the slit forming device 420 bythe rotation of the knife blades. Preferably, a drive mechanism havingsufficient power and timing capability (well known in the art) is usedto synchronize the rotation of the two axes at relatively the samerotational speed, regardless of loading by the action of slitting of thecomposite.

In a preferred embodiment, the knife roll comprises a plurality of knifeplates 430 as shown in FIG. 21. The plurality of knife plates aremounted on a drive shaft 423 (shown in FIG. 20) through shaft opening450 at the centerline of the blade. The individual knife blades 432 areconstructed and arranged on the blade plate to maintain a rotationalcenter of gravity at the centerline of the blade. A knife plate 430comprises a plurality of knife blades 432. Each knife blade comprises acutting portion 434 having a cutting tip 437, a leading edge 435 and atrailing edge 436. The cutting portion of the blade is that portionwhich can pass into the structure of the composite sheet 407 during theslitting process. The length of a knife blade, defined by x_(k), is themaximum length of the cutting portion 437 of the blade, from the leadingedge 435 to the trailing edge 436. The leading and trailing edges 435and 436 preferably are slightly rounded (radius about 0.5 mm) in orderto improve the separation of the trailing edge of the blade from theslitted composite by eliminating any corner on the blade which mightcatch the trailing edge of the slit.

Preferred knife blades of the present invention can be made of anymaterial which has a material hardness sufficient to cut the absorbentcomposite and sufficient strength to prevent bending, warping, flexing,or vibrating during the slitting operation. Preferably, an extremelyhard metallic or other material is used for longer wear and excellencein cutting performance. A preferred material is tungsten.

The thickness of the cutting portion of the blade, shown as z_(k) inFIG. 22 is preferably kept as thin a possible to reduce the resistancethrough the composite. The blade should be of sufficient thickness toprovide strength to prevent bending, warping, flexing, or vibrationduring the slitting operation. Preferably, the thickness of the cuttingportion is less than about I mm, more preferably less than about 0.5 mm.

The spacing between successive blades is shown as y_(k). Although theknife blade shown in FIG. 21 has six equally sized and spaced blades,knife plates can be used having a substantially greater number ofblades, and therefore a greater diameter and circumference. The spacingdistance between adjacent knife plates can be adjusted by placing one ofmore spacers 439 (FIG. 25), or shims, on the axis of the knife rollbetween adjacent knife blades to provide the appropriate spacing.

In a preferred embodiment, the continuous composite sheet 407 (FIG. 20)is partially tensioned in the cross-machine direction as the sheetenters the knife roll. The tensioning assists the cutting of thecomposite layers by the blades. In addition, the tensioning helps toreduce the friction of the cutting blades as they rotate out of theslits, due to the slightly shrinkage of the width of the compositesegments between adjacent blades as the tension is released uponslitting.

In a preferred embodiment of the method and apparatus, a means fordisengaging the slitting blades 432 from the slits of the slitted sheet408 is provided. A preferred disengaging means is a stripping plate 425shown in FIG. 25. The stripping plate 425 comprises a plurality ofparallel slots 429 extending there through. The length and width of eachslot, and the spacing between slots, accommodates the plurality of knifeblades of the knife roll 422. The blades 432 of the knife roll arepositioned to extend from the upper surface through the stripping plateslots 429 as shown in FIG. 25. The continuous composite sheet 407 isposition on the lower surface of the stripping plate 425. The strippingplate 425 has a trailing edge 428 which supports the slitted compositesheet as it separates from the knife roll 422. The stripping 425 plateis usually constructed from a metallic material, preferably stainlesssteel, and is of sufficient thickness to resist bending by the force ofthe slitted composite sheet when it is separated from the knife roll.

To assist in the stripping or separating of the slitted composite fromthe knife blades, a stripping layer material can be used. Such layer canbe a layer integral with the absorbent composite, for example a nonwovenlayer on the surface of the absorbent composite facing toward the kniferoll. The stripping layer can also be an independent layer that isregistered with the continuous composite prior to the slit forming step,and is separated from the slitted composite thereafter. An example ofsuch material can include nonwovens, plastic or metallic films, andwaxed or other treated substrates or paper. The stripping layer can alsohave a lubricating agent which can deposit on the blades to help resistbuildup of absorbent macrostructure and substrate material. Suchlubricants can be liquid or semi-solid, such as a wax or oil, or solidagent such as graphite. A preferred stripping layer is waxed paper.

The recess roll 424 has a series of grooves 441 as shown in FIG. 23which serve as guides for the blades 432 of the blade roll. The recessroll also serves to retain the absorbent composite sheet against theblade roll (and optionally, the stripping plate 425). There isessentially one groove for each blade plate. Groove 441 preferably has ashape and dimension to match the cutting tip 434 of the blades asclosely as possible. Most preferably, the recess roll is constructed ofa material that is as hard as possible, but will not cut or wear out theblade cutting tips 434. A preferred material for constructing the recessroll is nylon or Teflon. The grooves can be formed initially in therecess roll by touching or slightly pressing the rotating blade rollagainst the recess roll to set the track of the blades.

Other devices can used in place of a recess roll to provide the samefunction. For example, a stationary backing member having a series ofslots can also be used. An example of a stationary backing member is aslotted plate which resembles the stripping plate 425. The compositesheet 407 passes between the stripping plate 425 and the stationarybacking member. The blades of the blade roll rotate through the slots ofthe stripping plate and the stationary backing member, thereby cuttingthe slits in the sheet.

Individual recess plates corresponding in spacing and number to theblade plates can also be used in place of a recess roll.

It is also preferred to provides means for continuously cleaning theknife blades and the recess roll of substrate material and absorbentmacrostructure material that can build up. Such means can includebrushes, high pressure air streams, and other similar means well knownin the art.

In the absorbent composites of the present invention, the substratelayer 72 can comprise a material that is difficult to cut cleanlythrough, especially when the substrate is partially wet with liquid(from the composite making process). When wet, the substrate can stretchwhen impinged by the blade. In a preferred process of the presentinvention, the absorbent composite sheet 407 is passed through the slitforming device so that a substrate layer in the composite is orientedtoward the knife roll 422. This assists the knife blade to make acomplete slit through the substrate material. Furthermore, orienting thesubstrate toward the knife roll permits the substrate layer itself toassist in the separating of the absorbent composite, particularly theabsorbent macrostructure layer, from the knife blades after the slitshave been formed.

After a slitted absorbent composite is made, it can be collected andstored until needed. Typically it will be collected on a wind-up roll415 for transportation or storage.

The process of slitting the continuous sheet 407 itself can cause thewidth dimension of the slitted composite 408 to be increased. Inpreferred embodiments, where the spacing between parallel lines of slitsin the composite is very close, (for example, from 1 mm to 5 mm), thewidth dimension of the slitted sheet 408 can be from 5% to 10% greater,or more, than the width dimension of the starting non-slitted compositesheet 407.

Because of the crosslinking and bonding caused by the crosslinkingagent, it is preferred that the slitted absorbent sheet be partiallystretched before the wind-up roll. The amount of partial stretching willdepend upon the properties of the absorbent composite (such asthickness, etc.) and the slit pattern (such as, slit length). Usually,the slitted sheet is partially stretched between 1% and about 50% acrossthe width of the slits (i.e., stretched in the cross-machine directionfor slits that are oriented in the machine direction) before the wind-uproll, more preferably about 2%-15%. Partial stretching can beaccomplished by securing the longitudinal (machine-direction) edges ofthe sheet and pulling the secured edges apart, thereby stretching thesheet there between. Another preferred means comprises passing theslitted sheet over a stationary expanding device known as a flatexpander, manufactured by Shinko Co., Ltd. Osaka, Japan. Any means ofproviding, preferably continuously, extending or stretching the slittedsheet in the cross direction can be used.

The slitted composite, or the partially stretched slitted composite, isthen stretched in the cross-machine direction of the slits to form thefinished non-continuous composite. Any means (preferably continuous) forextending or stretching the slitted sheet in the cross-machine directioncan be used. The extent of stretching affects the opening size of thevoid formed by the slits, and therefore affects the percent void openingof the composite, to some extent. In a preferred embodiment, thelongitudinal (machine-direction) edges of the sheet are secured by acontinuous securing means and the securing means are extended apart,thereby stretching the sheet there between. In a continuous method forstretching the sheet, the secured edges are generally extended apartgradually so as to avoid tearing or non-uniform stretching of the sheet.A preferred method uses non-uniform cross-directional stretching toprovide the a stretched non-continuous composite with areas across thewidth which have been stretched to a greater extent than other areas.The degree of stretching affects the void opening size and therefore thepercentage of void openings in that portion of the composite.

The fully stretched non-continuous composite can itself be stored ortransported further, by collecting it on wind-up rolls, or, morepreferably, the stretched non-continuous absorbent composite is cut orseparated into unit sizes for further use in making an absorbentproduct, or for packaging or storage as an absorbent member. The cuttingor separating of the composite sheet into unit sizes can be made by avariety of means that are well known in the art, such as rotary orstationary cutting knives or blades, lasers, scoring and tearing,punching, etc. In a preferred method, a continuous sheet of stretchednon-continuous composite is cut into a plurality of unit widths usingrotary or stationary cutting knives or blades, each unit width ofcontinuous sheet is then further cut along its length into unit lengths,separated, and used in the making of an absorbent product.

Other methods of forming slits in a continuous composite can be used.Another method involves forming slits oriented in the cross-machinedirection. This method can be very similar to the method described abovefor making continuous slits in the machine direction. The blades arearranged in a predetermined pattern around the cylindrical surface ofthe knife roll, parallel with the axis of the roller, in thecross-direction. Typically, the blades will extend from the surface ofthe roller along a line passing though the axis of the roller. Anothermethod for forming a plurality of slits to through the composite in apredetermined pattern involves a batch slitting method. A composite isplaced on substantially rigid, flat cutting surface. A press platehaving a plurality of blades extending from the surface thereof in apredetermined pattern is positioned into a mechanical or hydraulicpress. When the predetermined pattern of blades of the press plate isforced by the press through the composite, for example by pressing theblades through the thickness of the composite, a pattern of slits isformed through the composite in the same predetermined pattern. Theblades will generally extend a distance from the surface of the pressplate that is at least the thickness of the composite, preferably more.Preferably, the press plate comprises a means for forcing the slittedcomposite off of the blades after slitting. Such means can compriseslots through which the blades pass, and can comprise a mechanical meanssuch as a spring-loaded plate, or a flexible, resilient means such as asolid foam sponge. Preferably, the cutting surface is a rigid, flatcutting surface that has recesses in the surface thereof which arematched with the extending blades in the press plate.

Another means of forming slits continuously in an absorbent composite islaser cutting.

A non-continuous composite can also be used in a method of forming aplurality of voids directly into a solid, continuous composite. Ingeneral, such a method is less preferred because it creates a by-productof void-sized composites that must be recycled, or used in some otherway to avoid the expense of scrapping. A continuous method is preferredfor forming a plurality of voids or openings into a continuous absorbentcomposite. Any punching or drilling technique and apparatus can be usedto make such voids. The voids are preferably formed in a predeterminedpattern and size. Methods for forming voids in sheet-like materials arewell-known in the art, and can be used for forming the non-continuouscomposites of the present invention.

C. Method for Making Semi-Continuous Absorbent Composites

A preferred method for making a semi-continuous absorbent compositeinvolves attaching, preferably bonding, a non-continuous to absorbentcomposite to a continuous layer, preferably a continuous substratelayer. The continuous layer can also be a continuous compositecomprising a substrate and a macrostructure layer. The method forattaching a continuous substrate to a non-continuous composite,(preferably a non-continuous absorbent macrostructure layer thereof)involves steps substantially the same as described above for attaching asubstrate to a continuous composite. Additional considerations includethe void openings in the non-continuous composite, and the need toretain a non-continuous composite or macrostructure layer in a stretchedstate while attaching the continuous substrate.

Another preferred method for forming a semi-continuous compositeinvolves cutting a plurality of voids out of an absorbent macrostructurelayer of a continuous composite of the present invention, withoutsubstantially penetrating the continuous layer, such as the substrate,thereof.

D. Embodiments of Methods for Making Absorbent Composites

(Preparation Example)

One hundred parts of precursor particles made in accordance with thePrecursor Particle Example are placed into a 5 quart standingkitchen-type mixer. The precursor particles have a particle size suchthat the precursor particles pass through a standard No. 50 sieve (300microns) and are retained on a standard No. 100 sieve (150 microns). Anaqueous treatment solution is prepared from a mixture of 4.3 partsKymene Plus (30% resin active), 2.6 parts water and 10.0 parts methanol.This treatment solution is sprayed onto the precursor particles with aPreval sprayer (available from The Precision Valve Corporation ofYonkers, N.Y.). The treatment solution is sprayed onto the precursorparticles, while the mixer is operating at slow speed, for a period ofabout 4 minutes, i.e. until all of the solution is sprayed onto theparticles. After spraying, the mixture of wet precursor particles ismixed at the highest speed setting for 2 to 5 minutes. During this highspeed mixing, the methanol is evaporated, thus increasing the stickinessof the treated mixture of precursor particles so that they will remainto adhered together. This sticky mixture of treated precursor particlesis then fed to an extrusion/compaction unit. The extruder screw has alength of 8 inches (20.3 cm) and contains 5 flights, each flight being1.5 inches (3.8 cm) in length. The outside diameter of the extruderscrew is 1.75 inches (4.45 cm) and the screw-to-housing clearance is0.20 inches (0.51 cm). The unit is activated such that the extruderscrew turns at a rate of 47 rpm. The mixture is extruded between twosmooth finish steel compaction rolls (nip rolls) with a fixed (butvariable) gap. The compaction rolls have a diameter of 8.975 inches(22.8 cm) and are driven at a rate of 5.4 rpm. The gap between thecompaction rolls is 0.015 inches (0.38 mm). The formed aggregate sheetsare then separated into approximately 12 to 15 inch (30 to 40 cm)lengths. The oven-cured sheets have a thickness (caliper) of about 0.031inches (0.8 mm) and a width of about 1.95 inches (4.95 cm). Aplasticizer solution containing 65 parts glycerol and 35 parts distilledwater is sprayed onto the oven-cured sheets at the rate of 0.9 g, ofplasticizer solution, per 1.0 g, of the oven-cured sheet. About 1/2 hourafter treatment with the plasticizer solution, the sheets havesufficient flexibility and tensile strength to be picked up.

CONTINUOUS COMPOSITES Example 1

In this example, 80 parts of precursor particles made in accordance withthe precursor particle example and having the particle sizecharacteristics described in Preparation are used. An aqueous treatmentsolution prepared from a mixture of 6.0 parts Kymene Plus (30% resinactive), 3.5 parts water and 8.5 parts glycerol is also used.

A reciprocating table or shuttle is used in conjunction with a pair ofsprayers that apply the treatment solution and a vibratory feeder thatdeposits the precursor particles. The sprayers and feeder are positionedabove the reciprocating surface of the table. Initially a substratematerial consisting of a double-ply Bounty® type sheet is placed ontothe surface of the table. Then, the table with the Bounty Sheet movesunderneath the sprayers, the treatment solution is sprayed onto thesurface of the Bounty Sheet (or layer of particles) in a predeterminedpattern. As the surface of the table moves further in the same directionand underneath the feeder, a predetermined amount of precursor particlesare deposited onto the Bounty Sheet surface (or previous layer oftreated particles in subsequent passes). After the particles have beendeposited from the feeder to form a layer thereof, the surface of thetable moves back in the opposite direction so that the sequence ofapplying treatment solution/depositing a layer of particles can berepeated.

In total, four layers of precursor particles (0.2 g/in² of particles perlayer) are deposited from the feeder. After each layer of precursorparticles has been deposited, a predetermined amount of the treatmentsolution is sprayed on top of each layer. The amount of treatmentsolution sprayed initially onto the surface of the table, as well as thefirst layer of precursor particles, is about 0.018 g/in². The amount oftreatment solution sprayed onto the other four layers of precursorparticles is about 0.036 g/in². In effect, each layer of precursorparticles is treated with the same amount of solution.

After the layering of precursor particles and spraying with treatmentsolution is complete, a relatively cohesive composite sheet of particlesis formed. This cohesive composite sheet is then fed by a belt to acompaction unit. The compaction unit consists of two coated steelcompaction rolls (nip rolls) with a fixed (but variable) gap. Thecompaction rolls have a diameter of about 8 inches (20 cm) and aredriven at a rate of about 20 rpm. The gap between the compaction rollsis about 0.05 inches (1.25 mm). The resultant aggregate composite sheets(density of 0.9-1.0 g/cc) are stored in plastic bags at ambient roomtemperature (about 65° C.-72° F., 18.3° C.-22.2° C.) for about 24 hours.During this ambient temperature curing, the Kymene Plus reacts with thepolymer material in the surface of the precursor particles, thus causingeffective crosslinking. The Kymene in the treatment solution also bondsto the cellulose structure of the Bounty Sheet and to the precursorparticles, the Bounty to the cohesive layers of particles therebybonding. The ambient temperature cured sheets have a thickness (caliper)of about 0.06-0.07 inches (1.5-1.8 mm) and a width of about 4 inches (10cm). These ambient temperature cured composite sheets have excellentflexibility and tensile strength, and can be handled easily withoutbreaking or tearing.

Example 2

In this example, apparatus 301 shown in FIG. 19 is used. The precursorparticles used are made in accordance with the precursor particleexample and have a size between 150-250 microns. An aqueous treatmentsolution is prepared from a mixture of 5.0 parts Kymene Plus (30% resinactive), 7.1 parts of water and 12.7 parts glycerol. Feeders 305 areSuper Feeder model #210 SE-00354 vibrating feeders, available fromSolids Flow Control, of Charlotte, N.C. Sprayers 304 are model 6218-1/4JAU atomized air actuated nozzle assemblies, available from SprayingSystems, Co., of Wheaton, Ill. For the first two applications, sprayers304a and 304b deliver the treatment solution to conveyor 303 at a rateof 39.8 grams/mm. For subsequent applications, sprayers 304c through304f deliver the treatment solution to conveyor 303 at a rate of 79.6grams/mm. Conveyor 303 is a moving conveyor made from polyurethane, andtravels at a speed of 27 ft./mm. Sheet feeder 313 includes a rolledsubstrate sheet consisting of a double-ply Bounty type sheet to supplythe Bounty sheet to conveyor 303 synchronized with the rate of conveyor303. The pressure applicators are a pair of compaction rolls 306 having8 inch (20 cm) diameters and being 12 inches (30.5 cm) wide. The top andbottom rolls 306 are coated with a #934 Plasma Coating, available fromPlasma Coatings, Inc., of Waterbury, Conn.

This example is carried out according to the following steps:

STEP 1: Supply the Bounty sheet to conveyor 303 in synchronization withthe rate of conveyor 303.

STEP 2: Spray a predetermined area of the surface of supplied Bountysheet with treatment solution in an amount substantially equal to 0.05grams of solution per square inch of the Bounty sheet.

STEP 3: Layer substantially continuously 0.2 grams of precursorparticles per square inch of the Bounty sheet onto the samepredetermined area.

STEP 4: The first layer of precursor particles on the predetermined areaof the Bounty sheet is sprayed with treatment solution in an amountsubstantially equal to 0.05 grams of solution per square inch of Bountysheet.

STEP 5: Layer substantially continuously 0.2 grams of precursorparticles per square inch of the Bounty sheet onto the samepredetermined area.

STEP 6: The second layer of precursor particles on the predeterminedarea of the Bounty sheet is sprayed with treatment solution in an amountsubstantially equal to 0.050 grams of solution per square inch of theconveyor.

STEP 7: Steps 5 and 6 are repeated, in order, 2 more times, giving: (a)a total of one initial spraying step and four post-layering sprayingsteps for a total of 0.25 grams of treatment solution per square inch ofthe Bounty sheet; and (b) a total of four layering steps for a total of0.8 gram of precursor particles per square inch of the Bounty sheet. Anabsorbent composite is now formed.

STEP 8: The absorbent composite is passed through the compaction rolls.The gap between the compaction rolls is 0.05 inches (1.25 mm). Thisproduces a sheet having a density of 0.995 g/cc.

STEP 9: The sheet is cured by placing it in a plastic bag and allowingit to sit at ambient temperature (72° F., 22.2° C.) for 48 hours.

The resultant absorbent composite sheet has good flexibility, dryintegrity properties, and free gel blocking.

Example 3

A continuous absorbent composite of Example 2 is placed onto a table sothat the absorbent macrostructure layer can face upward (the nonwovensheet is faced to the table). While passing the table under the Prevalsprayer, an amount substantially equal to 0.05 grams of solution persquare inch of the treatment solution is uniformly applied to thesurface of the absorbent macrostructure layer. Then, about 0.004 g/cm²of a polypropylene nonwoven sheet is registered with the adhesivesurface of the absorbent macrostructure layer, thereby forming acontinuous absorbent composite having a sandwich structure as shown inFIG. 2.

NON-CONTINUOUS COMPOSITES: Example 4

After preparing a cutting table, the continuous absorbent composite ofExample 2 is placed on a flat cutting surface. A punch cutter whichcomprises 20 cylindrical blades faced to outside is prepared. Each ofthe blades has a diameter of 10 mm and the distance between centers ofadjacent two blades is designed at 20 mm. The punch cutter is pusheddown on the continuous absorbent composite. Therefore, applying adequatepressure (about 0.5-5 kgf/cm 2) through the punch cutter to thecontinuous absorbent composite on the flat cutting surface, 20 ofcircular voids penetrating the composite can be formed in the absorbentcomposite. As a result, a non-continuous absorbent composite can beobtained.

Example 5

The continuous absorbent composite of Example 3 is placed on a flatcutting surface. A razor knife is used to cut a series of parallel linesof interlaced slits completely through the thickness of the continuousabsorbent composite, such that the slitted composite has the appearanceof FIG. 18. Each individual slit is about 20 mm long, and each slit in aline is separate from the start of the next slit by a slit spacing gapabout 5 mm distance. In a first line of slits, the centers of slits arepositioned opposite the centers of the slit spacing gaps of the nextline. Each parallel line is spaced across the width of the composite adistance of about 0.2 cm from the next line. After the composite hasbeen slit by means of the razor knife, one of the end edges which isparallel with the lines of slits is secured. The other end edge isgrasped and is pulled slowly in the perpendicular direction away fromthe first end edge until the width of the stretched, shifted compositeis approximate 1.5-3.0 time of the original width, thus forming thenon-continuous composite as shown in FIG. 9.

Example 6

In this example, slit forming device 420 substantially as shown in FIG.20 is used to form a slitted absorbent composite sheet from acontinuous, non-slitted sheet made in accordance with Example 2. Theknife roll 422 consists of 50 (fifty) identical knife bladessubstantially as shown in FIG. 21. Each knife blade has six bladeshaving a length x_(k) of 20.0 mm, a blade spacing y_(k) of 4.0 mm, ablade thickness z_(k) of 0.3 mm, and a blade diameter of about 45 mm.Each knife blade is made of tungsten. Alternating knife blades areinverted when mounted on the shaft 423 so that the blades thereof areoffset from the blade of the adjacent plate by about 15°. Shims 439 areplaced between adjacent knife blades to separate the planes of the bladetips by a distance of 1.9 mm. Recess roll 424 is constructed of a Teflonmaterial and has a matching recess 441 for each knife blade. Thestripping plate 425 is made of stainless steel of 3 mm thickness.

To assist in the stripping of the slitted composite from the knifeblades, a sheet of waxed paper (approximately 2 mil, 0.050 mm) isregistered on both surfaces of the absorbent composite prior toslitting. The absorbent composite is fed into the opening 421 betweenthe stripping plate 425 and the recess roll 424 with the Bounty®substrate layer facing downward toward the knife roll. Two 100 mmoutside diameter air cylinders are used to force the knife roll upwardwith an air pressure of 2.5 kg to 5 kg force per square centimeter. Theresulting slitted composite is partially stretched (about 15%) afterexisting the slit forming device. A non-continuous "netted" composite isthen formed by stretching the width (cross-machine direction) of theslitted composite uniformly by 100%.

SEMI-CONTINUOUS COMPOSITES Example 7

After preparing a cutting table, a continuous absorbent sheet ofPreparation Example is placed on a flat cutting surface. A punch cutterwhich comprises 20 circular blades faced to outside is prepared. Each ofthe blades has a diameter of 10 mm and the distance between centers ofadjacent two blades is designed at 20 mm. The punch cutter is pusheddown on the continuous absorbent composite. Therefore, applying adequatepressure (about 0.5-5 kgf/cm²) through the punch cutter to thecontinuous absorbent sheet on the flat cutting surface, 20 of circularvoids penetrating the composite can be formed in the absorbent sheet. Asa result, a non-continuous absorbent sheet can be formed.

A double-ply Bounty sheet having the same size as the non-continuousabsorbent sheet is prepared and the treatment solution is also sprayedonto the Bounty sheet with the Preval sprayer. After the cellulosicmaterial of the surface of the Bounty sheet is treated with a sufficientamount (e.g. an amount substantially equal to 0.05 grams of solution persquare inch ) of the treatment solution uniformly, the non-continuousabsorbent sheet is placed on the surface of the Bounty sheet. The twosheets are extruded into the compaction rolls and are applied anopposing pressure thereby. As a result, a semi-continuous absorbentcomposite can be obtained.

USES OF ABSORBENT COMPOSITES

The continuous, non-continuous, and semi-continuous absorbent composites(hereinafter, generally referred to simply as absorbent compositesunless specification identified otherwise) can be used for many purposesin many fields of use. For example, the absorbent composites can be usedfor packing containers; drug delivery devices; wound cleaning devices;burn treatment devices; ion exchange column materials; constructionmaterials; agricultural or horticultural materials such as seed sheetsor water-retentive materials; and industrial uses such as sludge or oildewatering agents, materials for the prevention of dew formation,desiccants, and humidity control materials.

Because of the unique absorbent properties of the porous, absorbentmacrostructures used in absorbent composites of the present invention,they are especially suitable for use as absorbent cores in absorbentarticles, especially disposable absorbent articles. As used herein, theterm "absorbent article" refers to articles which absorb and containbody exudates and more specifically refers to articles which are placedagainst or in proximity to the body of the wearer to absorb and containthe various exudates discharged from the body. Additionally,"disposable" absorbent articles are those which are intended to bediscarded after a single use (i.e., the original absorbent article inits whole is not intended to be laundered or otherwise restored orreused as an absorbent article, although certain materials or all of theabsorbent article may be recycled, reused, or composted). A preferredembodiment of a disposable absorbent article, diaper 20, is shown inFIG. 26. As used herein, the term "diaper" refers to a garment generallyworn by infants and incontinent persons that is worn about the lowertorso of the wearer. It should be understood, however, that the presentinvention is also applicable to other absorbent articles such asincontinent briefs, incontinent pads, training pants, diaper inserts,sanitary napkins, facial tissues, paper towels, and the like.

The non-continuous absorbent composites, preferably the net-like shapeabsorbent composite, and preferably comprising 90% or more by weight ofabsorbent gelling particles in the absorbent macrostructures, providehighly absorbent, thin and flexible absorbent cores. When using theabsorbent composites of the present invention as absorbent cores, verythin and flexible diapers and other absorbent articles can be obtained.Especially, use of the non-continuous absorbent composites, preferablynet-like shape absorbent composites in a diaper provides highly flexibleabsorbent cores. Consequently, use of the non-continuous absorbentcomposites of the present invention can provide diapers and otherabsorbent articles with high absorbency, thinness and flexibility.

FIG. 26 is a perspective view of the diaper 20 of the present inventionin its uncontracted state (i.e., with all the elastic inducedcontraction removed) with portions of the structure being cut-away tomore clearly show the construction of the diaper 20 and with the portionof the diaper 20 which contacts the wearer facing the viewer. The diaper20 is shown in FIG. 26 to preferably comprise a liquid pervious topsheet38; a liquid impervious backsheet 40 joined with the topsheet 38; anabsorbent core 42 positioned between the topsheet 38 and the backsheet40; elastic members 44; and tape tab fasteners 46. Preferably, thediaper 20 further comprises a tissue interposed at least between theabsorbent core 42 and the topsheet 38, more preferably provided toenclose the absorbent core 42. The topsheet 38, the backsheet 40, theabsorbent composite core 42, the elastic members 44 and the tissue canbe assembled in a variety of well known configurations. Absorbentcomposite core 42 can be selected from any continuous, non-continuous orsemi-continuous absorbent composite disclosed herein. Preferably,absorbent composite core 42 comprises a non-continuous absorbentcomposite, more preferably a net-like shape absorbent composite, asshown in FIG. 26.

A preferred diaper configuration for a diaper comprising an absorbentcomposite core 42 is described generally in U.S. Pat. No. 3,860,003(Buell), issued Jan. 14, 1975, which is incorporated by reference.Alternatively preferred configurations for disposable diapers herein arealso disclosed in U.S. Pat. No. 4,808,178 (Aziz et al), issued Feb. 28,1989; U.S. Pat. No. 4,695,278 (Lawson), issued Sep. 22, 1987; U.S. Pat.No. 4,816,025 (Foreman), issued Mar. 28, 1989; and U.S. Pat. No.5,15,092 (Buell et al.), issued Sep. 29, 1992, all of which areincorporated by reference.

FIG. 26 shows a preferred embodiment of the diaper 20 in which thetopsheet 38 and the backsheet 40 are co-extensive and have length andwidth dimensions generally larger than those of the absorbent compositecore 42. The topsheet 38 is joined with and superimposed on thebacksheet 40 thereby forming the periphery of the diaper 20. Theperiphery defines the outer perimeter or the edges of the diaper 20. Theperiphery comprises the end edges 32 and the longitudinal edges 30.

The absorbent composite core 42 is also preferably used as an absorbentmeans in pull-on diapers, such as those disclosed in U.S. Pat. No.5,074,854 (Davis), issued Dec. 24, 1991, which is incorporated byreference.

The topsheet 38 is compliant, soft feeling, and non-irritating to thewearer's skin. Further, the topsheet 38 is liquid pervious permittingliquids to readily penetrate through its thickness. A suitable topsheet38 can be manufactured from a wide range of materials such as porousfoams, reticulated foams, apertured plastic films, natural fibers (e.g.,wood or cotton fibers), synthetic fibers (e.g., polyester orpolypropylene fibers) or from a combination of natural and syntheticfibers. Preferably, the topsheet 38 is made of a hydrophobic material toisolate the wearer's skin from liquids in the absorbent core 42.

A particularly preferred topsheet 38 comprises staple lengthpolypropylene fibers having a denier of about 1.5, such as Hercules type151 polypropylene marketed by Hercules, Inc. of Wilmington, Del. As usedherein, the term "staple length fibers" refers to those fibers having alength of at least about 15.9 mm (0.62 inches).

There are a number of manufacturing techniques which can be used tomanufacture the topsheet 38. For example, the topsheet 38 can be woven,nonwoven, spunbonded, carded, or the like. A preferred topsheet iscarded, and thermally bonded by means well known to those skilled in thefabrics art. Preferably, the topsheet 38 has a weight from about 18 toabout 25 grams per square meter, minimum dry tensile strength of atleast about 400 grams per centimeter in the machine direction, and a wettensile strength of at least about 55 grams per centimeter in thecross-machine direction.

The backsheet 40 is impervious to liquids and is preferably manufacturedfrom a thin plastic film, although other flexible liquid imperviousmaterials may also be used. The backsheet 40 prevents the exudatesabsorbed and contained in the absorbent core 42 from wetting articleswhich contact the diaper 20 such as bedsheets and undergarments.Preferably, the backsheet 40 is polyethylene film having a thicknessfrom about 0.012 (0.5 mil) to about 0.051 centimeters (2.0 mils),although other flexible, liquid impervious materials can be used. Asused herein, the term "flexible" refers to materials which are compliantand which will readily conform to the general shape and contours of thewearer's body.

A suitable polyethylene film is manufactured by Monsanto ChemicalCorporation and marketed in the trade as Film No. 8020. The backsheet 40is preferably embossed and/or matte finished to provide a more clothlikeappearance. Further, the backsheet 40 may permit vapors to escape fromthe absorbent core 42 while still preventing exudates from passingthrough the backsheet 40.

The size of the backsheet 40 is dictated by the size of the absorbentcore 42 and the exact diaper design selected. In a preferred embodiment,the backsheet 40 has a modified hourglass-shape extending beyond theabsorbent core 42 a minimum distance of at least about 1.3 centimetersto about 2.5 centimeters (about 0.5 to about 1.0 inch) around the entirediaper periphery.

The topsheet 38 and the backsheet 40 are joined together in any suitablemanner. As used herein, the term "joined" encompasses configurationswhereby the topsheet 38 is directly joined to the backsheet 40 byaffixing the topsheet 38 directly to the backsheet 40, andconfigurations whereby the topsheet 38 is indirectly joined to thebacksheet 40 by affixing the topsheet 38 to intermediate members whichin turn are affixed to the backsheet 40. In a preferred embodiment, thetopsheet 38 and the backsheet 40 are affixed directly to each other inthe diaper periphery by attachment means (not shown) such as an adhesiveor any other attachment means as known in the art. For example, auniform continuous layer of adhesive, a patterned layer of adhesive, oran array of separate lines or spots of adhesive can be used to affix thetopsheet 38 to the backsheet 40.

Tape tab fasteners 46 are typically applied to the .back waistbandregion of the diaper 20 to provide a fastening means for holding thediaper on the wearer. The tape tab fasteners 46 can be any of those wellknown in the art, such as the fastening tape disclosed in U.S. Pat. No.3,848,594 (Buell), issued Nov. 19, 1974, which is incorporated byreference. These tape tab fasteners 46 or other diaper fastening meansare typically applied near the corners of the diaper 20.

The elastic members 44 are disposed adjacent the periphery of the diaper20, preferably along each longitudinal edge 30, so that the elasticmembers 44 tend to draw and hold the diaper 20 against the legs of thewearer. Alternatively, the elastic members 44 can be disposed adjacenteither or both of the end edges 32 of the diaper 20 to provide awaistband as well as or rather than leg cuffs. For example, a suitablewaistband is disclosed in U.S. Pat. No. 4,515,595 (Kievit et al), issuedMay 7, 1985, which is incorporated by reference. In addition, a methodand apparatus suitable for manufacturing a disposable diaper havingelastically contractible elastic members is described in U.S. Pat. No.4,081,301 (Buell), issued Mar. 28, 1978, which is incorporated byreference.

The elastic members 44 are secured to the diaper 20 in an elasticallycontractible condition so that in a normally unrestrained configuration,the elastic members 44 effectively contract or gather the diaper 20. Theelastic members 44 can be secured in an elastically contractiblecondition in at least two ways. For example, the elastic members 44 canbe stretched and secured while the diaper 20 is in an uncontractedcondition. Alternatively, the diaper 20 can be contracted, for example,by pleating, and the elastic members 44 secured and connected to thediaper 20 while the elastic members 44 are in their unrelaxed orunstretched condition.

In the embodiment illustrated in FIG. 26, the elastic members 44 extendalong a portion of the length of the diaper 20. Alternatively, theelastic members 44 can extend the entire length of the diaper 20, or anyother length suitable to provide an elastically contractible line. Thelength of the elastic members 44 is dictated by the diaper design.

The elastic members 44 can be in a multitude of configurations. Forexample, the width of the elastic members 44 can be varied from about0.25 millimeters (0.01 inches) to about 25 millimeters (1.0 inch) ormore; the elastic members 44 can comprise a single strand of elasticmaterial or can comprise several parallel or non-parallel strands ofelastic material; or the elastic members 44 can be rectangular orcurvilinear. Still further, the elastic members 44 can be affixed to thediaper in any of several ways which are known in the art. For example,the elastic members 44 can be ultrasonically bonded, heat and pressuresealed into the diaper 20 using a variety of bonding patterns or theelastic members 44 can simply be glued to the diaper 20.

The absorbent composite core 42 of the diaper 20 is positioned betweenthe topsheet 38 and the backsheet 40. The absorbent composite core 42can be manufactured in a wide variety of sizes and shapes (e.g.,rectangular, hourglass, asymmetrical, etc.). The total absorbentcapacity of the absorbent core 42 should, however, be compatible withthe design liquid loading for the intended use of the absorbent articleor diaper. The size and absorbent capacity of the absorbent compositecore 42 can vary to accommodate wearers ranging from infants throughadults.

As shown in FIG. 27, another preferred embodiment of the diaper 20 has arectangular-shaped absorbent composite core 42 comprising anon-continuous absorbent composite of the present unit, wherein thecomposite has an absorbent macrostructure layer 71 and a substrate layer72, and has voids 85 penetrating therein.

Alternatively, the absorbent cores 42 of the present invention canconsist solely of one or more absorbent composites of the presentinvention; can comprise a combination of the absorbent composites of thepresent invention; or any other absorbent core configurations includingone or more of the absorbent composite of the present invention.

An alternative embodiment of the diaper 120 comprising an absorbentassembly 60 comprising, an hourglass-shaped non-continuous absorbentcomposite 42 and an acquisition component 62. The acquisition component62 can be positioned above the absorbent composite core 42, below theabsorbent composite core 42, and both above and below the absorbentcomposite core 42. FIG. 28 shows such as diaper 120 having anacquisition means 62 positioned above the absorbent composite core 42(i.e., between the absorbent composite core 42 and the topsheet 38).Preferably, the diaper 120 further comprises a tissue interposed atleast between the absorbent composite core 42 and the topsheet 38, morepreferably provided to enclose the absorbent composite core 42. In apreferred embodiment an acquisition means 62 is positioned both aboveand below the non-continuous, composite core 42.

Acquisition component 62 serves to quickly collect and temporarily holddischarged liquids and to transport such liquids by wicking from thepoint of initial contact to other parts of the acquisition component 62and to the absorbent composite core 42. The acquisition component 62preferably comprises a web or batt of fiber materials. Various types offiber material can be used in the acquisition component 62. Cellulosicfibers are generally preferred for use herein, wood pulp fibers beingespecially preferred. More preferably, chemically stiffened cellulosicfibers, air felt fibers, synthetic fibers, large cell hydrophilicabsorbent foam materials or a mixture thereof can be used as theacquisition means 62. The acquisition component 62 can also containspecific amounts of a particulate, absorbent, polymeric composition. Theacquisition component 62, for example, can contain up to about 50% byits weight of the polymeric composition. In the most preferredembodiments, the acquisition component 62 contains from 0% to about 8%by its weight of a particulate, absorbent, polymeric composition.Exemplary embodiments of the acquisition component 62 useful in thepresent invention are described in U.S. Pat. No. 4,673,402 (Weisman etal), issued Jun. 16, 1987; and U.S. Pat. No. 4,834,735 (Alemany et al),issued May 30, 1989, both of which are incorporated by reference. Anacquisition component having a storage zone and an acquisition zone witha lower average density and a lower average basis weight per unit areathan the storage zone so that the acquisition zone can effectively andefficiently rapidly acquire discharged liquid are especially preferredfor use herein.

The acquisition component 62 can be of any desired shape, for example,rectangular, oval, oblong, asymmetric or hourglass-shaped. The shape ofthe acquisition component 60 can define the general shape of theresulting diaper 120. The acquisition component 60 of the presentinvention need not be the same size as the absorbent composite core 42,and can, in fact, have a top (or bottom) surface area which issubstantially smaller or larger than the top (or bottom) surface area ofthe absorbent composite core 42. In a preferred embodiment comprising anon-continuous (for example, a "netted") absorbent composite, theacquisition component 62 and the absorbent composite 42 are preferablycompressed together.

In alternatively preferred embodiments, a plurality of absorbentcomposite core sheets, preferably from two to six sheets in the form ofstrips, can be substituted for the single absorbent composite core 42.The plurality of absorbent composite sheets can be arranged in anypattern though preferably parallel and in the longitudinal direction ofthe diaper.

By spacing absorbent composite strips from one another, a more effectivesurface area is presented for acquiring and holding the dischargeliquids. This is particularly true since the spaced absorbent compositestrips can swell and expand in the direction of their width, withoutinterfering with the ability of adjacent strips to acquire dischargedliquids.

The absorbent composite core 42 can also be used as an absorbent meansin catamenial absorbent products. Since products generally comprise aliquid pervious topsheet overlaying the absorbent means, and a liquidimpervious backsheet on the opposing surface of the absorbent means. Thetopsheet and backsheet can be selected from materials as describedherein above. Preferred catamenial products comprise a formed-film,apertured topsheet as disclosed in U.S. Pat. No. 4,285,343 (McNair),issued Aug. 25, 1981; U.S. Pat. No. 4,608,047 (Mattingly), issued Aug.26, 1986; and U.S. Pat. No. 4,687,478 (Van Tilburg), issued Aug. 18,1987, all of which are incorporated by reference.

Preferred catamenial products can comprise wings, side flaps, and otherstructures and elements, as described in co-pending, commonly-assignedU.S. application Ser. No. 984,071, to Yasuko Morita, entitled "AbsorbentArticle Having Elasticized Side Flaps ", Attorney Docket No. JA-09RM,filed Nov. 30, 1992, incorporated herein by reference.

TEST METHODS

Synthetic Urine

The specific synthetic urine used in the test methods of the presentinvention is referred to herein as "Synthetic Urine". The SyntheticUrine is commonly known as Jayco SynUrine and is available from JaycoPharmaceuticals Company of Camp Hill, Pa. The formula for the SyntheticUrine is: 2.0 g/l of KCl; 2.0 g/l of Na2SO4; 0.85 g/l of (NH4)H2PO4;0.15 g/l (NH4)2HPO4; 0.19 g/l of CaCl2 and 0.23 g/l of MgCl2. All of thechemicals are of reagent grade. The pH of the Synthetic Urine is in therange of 6.0 to 6.4.

A. Absorptive Capacity of the Precursor Particles

The polymeric composition is placed within a "tea bag", immersed in anexcess of Synthetic Urine for a specified period of time, and thencentrifuged for a specific period of time. The ratio of polymericcomposition final weight after centrifuging minus initial weight (netfluid gain) to initial weight determines the Absorptive Capacity.

The following procedure is conducted under standard laboratoryconditions at 23° C. (73° F.) and 50% relative humidity. Using a 6 cm×12cm cutting die, the tea bag material is cut, folded in half lengthwiseand sealed along two sides with a T-bar sealer to produce a 6 cm×6 cmtea bag square. The tea bag material utilized is a grade 1234 heatsealable material, obtainable from C. H. Dexter, Division of the DexterCorp., Windsor Locks, Conn., U.S.A., or equivalent. Lower porosity teabag material should be used if required to retain fine particles. 0.200grams plus or minus 0.005 grams of the polymeric composition is weighedonto a weighing paper and transferred into the tea bag, and the top(open end) of the tea bag is sealed. An empty tea bag is sealed at thetop and is used as a blank. Approximately 300 milliliters of SyntheticUrine are poured into a 1,000 milliliter beaker. The blank tea bag issubmerged in the Synthetic Urine. The tea bag containing the polymericcomposition (the sample tea bag) is held horizontally to distribute thematerial evenly throughout the tea bag. The tea bag is laid on thesurface of the Synthetic Urine. The tea bag is allowed to wet, for aperiod of no more than one minute, and then is fully submerged andsoaked for 60 minutes. Approximately 2 minutes after the first sample issubmerged, a second set of tea bags, prepared identically to the firstset of blank and sample tea bags, is submerged and soaked for 60 minutesin the same manner as the first set. After the prescribed soak time iselapsed, for each set of tea bag samples, the tea bags are promptlyremoved (using tongs) from the Synthetic Urine. The samples are thencentrifuged as described below. The centrifuge used is a Delux Dynac IICentrifuge, Fisher Model No. 05-100-26, obtainable from FisherScientific Co. of Pittsburgh, Pa., or equivalent. The centrifuge shouldbe equipped with a direct read tachometer and an electric brake. Thecentrifuge is further equipped with a cylindrical insert basket havingan approximately 2.5 inch (6.35 cm) high outer wall with an 8.435 inch(21.425 cm) outer diameter, a 7.935 inch (20.155 cm) inside diameter,and 9 rows each of approximately 106 3/32 inch (0.238 cm) diametercircular holes equally spaced around the circumference of the outerwall, and having a basket floor with six 1/4 inch (0.635) cm) diametercircular drainage holes equally spaced around the circumference of thebasket floor at a distance of 1/2 inch (1.27 cm) from the interiorsurface of the outer wall to the center of the drainage holes, or anequivalent. The basket is mounted in the centrifuge so as to rotate, aswell as brake, in unison with the centrifuge. The sample tea bags arepositioned in the centrifuge basket with a folded end of the tea bag inthe direction of the centrifuge spin to absorb the initial force. Theblank tea bags are placed to either side of the corresponding sample teabags. The sample tea bag of the second set must be placed opposite thesample tea bag of the first set; and the blank tea bag of the second setopposite the blank tea bag of the first set, to balance the centrifuge.The centrifuge is started and allowed to ramp up quickly to a stablespeed of 1,500 rpm. Once the centrifuge has been stabilized at 1,500rpm, a tinier is set for 3 minutes. After 3 minutes, the centrifuge isturned off and the brake is applied. The first sample tea bag and thefirst blank tea bag are removed and weighed separately. The procedure isrepeated for the second sample tea bag and the second blank tea bag. TheAbsorptive Capacity (ac) for each of the samples is calculated asfollows: ac=(sample tea bag weight after centrifuge minus blank tea bagweight after centrifuge minus dry polymeric composition weight) dividedby (dry polymeric composition weight). The Absorptive Capacity value foruse herein is the average Absorptive Capacity of the two samples.

B. Fluid Stability

The objective of this method is to determine the stability ofmacrostructure aggregates and absorbent composites of the presentinvention upon exposure to Synthetic Urine.

The sample macrostructure or absorbent composite is placed in a shallowdish. An excess amount of Synthetic Urine is added to the macrostructureor absorbent composite.

The swelling of the macrostructure or absorbent composite is observeduntil equilibrium is reached. During the observation of the swellingmacrostructure or absorbent composite, the macrostructure or absorbentcomposite is observed for small particles breaking off from the mainabsorbent aggregate, platelet-like particles floating away from the mainabsorbent aggregate, or particles breaking and floating away from themain absorbent aggregate. If the absorbent aggregate has a large numberof broken away component particles, the macrostructure or absorbentcomposite is considered unstable. The macrostructure or absorbentcomposite should also be observed for isotropic swelling. If theabsorbent aggregate remains relatively stable and the relative geometryand spatial relationships of the precursor particles and the pores aremaintained after the test procedure, the macrostructure or absorbentcomposite is considered stable. Preferably, fluid stable macrostructuresor absorbent composites are capable of being picked up in their swollenstate without breaking apart.

C. Precursor Particle Size and Mass Average Particle Size

The particle size distribution on a weight percent basis of a 10 grambulk sample of the precursor particles is determined by sieving thesample through a set of 19 sieves ranging in size from a standard #20sieve (850 microns) through a standard #400 sieve (38 microns). Thesieves are standard sieves as obtainable from the Gilson Company, Inc.of Worthington, Ohio. The procedure is carried out on three stacks ofsieves at a time since the equipment used cannot hold all 19 sieves atone time. A first stack contains sieves #20, 25, 30, 35, 40, 45, and 50plus the sieve pan; the second stack contains sieves #60, 70, 80, 100,120, and 140 plus the sieve pan; the third stack contains sieves #170,200, 230, 270, 325, and 400 plus the sieve pan. The precursor particlesremaining on each of these sieves are then weighed to determine theparticle size distribution on a weight percent basis.

The first stack of sieves is mounted on a shaker and 10.0 grams plus orminus 0.00 grams of the sample is placed on the #20 sieve. The shakerused is a Vibratory 3-inch Sieve Shaker Model SS-5 as obtainable fromthe Gilson Company, Inc. of Worthington, Ohio. The stack is shaken for 3minutes at approximately 2100 vibrations per minute ("6" on theinstrument dial). The sieve pan is then removed and the stack set asidefor later weighing. Using a soft brush, the sample remaining on thesieve pan is transferred onto a weighing paper. The second stack ofsieves is mounted on the shaker and the sample on the weighing paper istransferred onto the #60 sieve. The second stack is shaken for 3 minutesat approximately 2100 vibrations per minute, the sample remaining on thesieve pan being transferred to a weighing paper and the stack set aside.The third stack of sieves is mounted on the shaker and the sample on theweighing paper is transferred onto the #170 sieve. The third stack isshaken for 3 minutes at approximately 2100 vibrations per minute. A softbrush is used to transfer the contents of each given sieve onto a taredweighing paper. The sample is weighed on a standard three place scaleand the weight of the sample on the specific sieve is recorded. Thisstep is repeated, using a fresh weighing paper for each sample, for eachsieve, and for the sample remaining on the sieve pan after the thirdstack of sieves has been shaken. The method is repeated for twoadditional 10 gram samples. The average of the weights of the threesamples for each sieve determine the average particle size distributionon a weight percent basis for each sieve size.

The Mass Average Particle Size of the 10 gram bulk sample is calculatedas follows:

    maps=Σ(Di×Mi)/ΣMi

wherein maps is the mass average particle size; Mi is the weight of theparticles on the specific sieve; and Di is the "size parameter" for thespecific sieve. The size parameter, Di of a sieve is defined to mean thesize (in microns) of the next highest sieve. For example, a standard #50sieve has a size parameter of 355 microns, which corresponds to the sizeof the openings in a standard #45 sieve (the next highest sieve). TheMass Average Particle Size for use herein is the average of the massaverage particle size of the three samples.

Precursor Particle Example

A jacketed 10 liter twin arm stainless steel kneader measuring 220mm×240 mm in the opening and 240 mm in depth, and having two Sigma typeblades possessing a rotational diameter of 120 mm is sealed with a lid.An aqueous monomer solution is prepared consisting of 37 weight %monomer. The monomer consists of 75 mole % sodium acrylate and 25 mole %acrylic acid. 5500 grams of the aqueous monomer solution is charged tothe kneader vessel, which is subsequently purged with nitrogen gas toremove the remaining entrapped air. Then, the two Sigma type blades areset rotating at rates of 46 rpm and the jacket is heated by the passageof 35° C. water. 2.8 g of sodium persulfate and 0.14 g of L-ascorbicacid are added as polymerization initiators. Polymerization begins aboutfour minutes after the addition of the initiators. A peak temperature of82° C. is reached inside the reaction system 15 minutes after theaddition of the initiators. The hydrated gel polymer is divided intoparticles about 5 mm in size as the stirring is continued. The lid isremoved from the kneader 60 minutes after the start of thepolymerization and the material is removed from the kneader.

The resultant hydrated aqueous gel polymer thus obtained is spread on astandard #50 size metal gauze and dried with hot air at 150° C. for 90minutes. The dried particles are pulverized with a hammer type crusherand sifted with a standard #20 sieve (850 microns) to obtain particlesthat pass through the standard #20 sieve. The mass average particle sizeof these particles is 405 microns.

D. Measurement of Wicking Ratio and Wicking Distance for AbsorbentComposites

The fluid wicking rate or speed and wicking distance of absorbentcomposites are measured in the following. After preparing an absorbentcomposite having a width of 2 cm and a length of 30 cm, the absorbentcomposite is attached to a parafilm compartment so that one end of theabsorbent composite juts out from the parafilm compartment at 1 cmlength. The parafilm compartment has edges sealed to prevent anyevaporation. After filling a vessel with the Synthetic Urine, theparafilm compartment is hung on the vessel to put the jutting portion (1cm) of the end of the absorbent composite in the Synthetic Urine. Afterthe start of the test, the fluid advancement is recorded every tenseconds. The wicking rate is determined by the advanced distance after 4minutes period. Also, the wicking distance is determined by the lastdistance at 20 hours after from the start of recording. This measurementis carried out under the normal room temperature (about 25° C.).

What is claimed is:
 1. An absorbent composite comprising:(a) at leastone absorbent macrostructure layer comprising a multiplicity ofinterconnected absorbent gelling particles, wherein at least a portionof the surfaces of said particles are crosslinked, and (b) at least onemeans bonded to said absorbent macrostructure layer by a crosslinkingagent capable of crosslinking said particles for distributing liquid tobe absorbed by said absorbent macrostructure layer.
 2. The absorbentcomposite according to claim 1 wherein said crosslinking agent is acationic amino-epichlorohydrin adduct.
 3. An absorbent compositecomprising:(a) at least one absorbent macrostructure layer comprising amultiplicity of interconnected absorbent gelling particles, wherein atleast a portion of the surfaces of said particles are crosslinked, and(b) at least one support bonded to said absorbent macrostructure layerby a crosslinking agent capable of crosslinking said particles.
 4. Theabsorbent composite according to claim 3 wherein said crosslinking agentis a cationic amino-epichlorohydrin adduct.
 5. The absorbent compositeaccording to claim 4 wherein said crosslinking is a cationic polymericamino-epichlorohydrin resin.
 6. The absorbent composite according toclaim 5 further comprising at least one means bonded to said absorbentmacrostructure layer for distributing liquid to be absorbed by saidabsorbent macrostructure layer.
 7. An absorbent composite comprising:(a)a first absorbent macrostructure layer having a first and a secondsurface, comprising a multiplicity of interconnected absorbent gellingparticles, wherein at least a portion of the surfaces of said particlesare crosslinked, and (b) a first substrate having a first surface bondedto said first surface of said first absorbent macrostructure layer by acrosslinking agent capable of crosslinking said particles.
 8. Theabsorbent composite according to claim 7 further comprising:(c) a secondsubstrate having a first surface bonded to said second surface of saidabsorbent macrostructure layer by said crosslinking agent.
 9. Theabsorbent composite according to claim 7 further comprising:(d) a secondabsorbent macrostructure layer having a first surface bonded to a secondsurface of said first substrate.
 10. An absorbent compositecomprising:(a) a plurality of absorbent macrostructure layers, eachlayer having a first and a second surface and comprising a multiplicityof interconnected absorbent gelling particles, wherein at least aportion of the surfaces of said particles are crosslinked, and (b) aplurality of substrates interposed alternately between said plurality ofabsorbent macrostructure layers and bonded thereto by a crosslinkingagent capable of crosslinking said particles.
 11. The absorbentcomposite according to claim 10 wherein said crosslinking agent is acationic amino-epichlorohydrin adduct.
 12. The absorbent compositeaccording to claim 11 wherein said substrate is a cellulosic material,and wherein said substrate is chemically bonded to said surface of saidabsorbent macrostructure layer by said cationic amino-epichlorohydrinadduct.
 13. The absorbent composite according to claim 12 wherein saidsubstrate comprises a plurality of capillary elements having a lengthfor distributing liquid therethrough along said length.
 14. Theabsorbent composite according to claim 12 wherein said particles have amass average particle size of from about 20 microns to about 1500microns.
 15. The absorbent composite according to claim 12 wherein saidparticles have substantially the same mass average particle size. 16.The absorbent composite according to claim 12 wherein said absorbentmacrostructure layer comprises from about 50% to about 100% by weight ofsaid particles.
 17. The absorbent composite according to claim 12wherein said absorbent macrostructure layer comprises a plurality ofparticle layers, wherein at least two adjacent particle layers havesubstantially different particle properties.
 18. The absorbent compositeaccording to claim 17 wherein said particles have a different massaverage particle size in each of said adjacent layers.
 19. The absorbentcomposite according to claim 12 wherein said absorbent macrostructurelayer has an average basis weight of from about 100 g/m² to about 1500g/m² and a density of from about 0.6 g/cc to about 1.1 g/cc.
 20. Theabsorbent composite according to claim 19 wherein said average basisweight is from about 250 g/m² to about 1200 g/m².
 21. The absorbentcomposite according to claim 20 wherein said absorbent macrostructurelayer is in the form of a sheet.
 22. The absorbent composite accordingto claim 12 wherein said absorbent macrostructure layer furthercomprises a plasticizer.
 23. The absorbent composite according to claim21 wherein said plasticizer is from about 5 parts to about 100 parts byweight, per 100 parts by weight of said absorbent gelling particles. 24.The absorbent composite according to claim 23 wherein said plasticizercomprises glycerol or a mixtures of glycerol and water.
 25. Theabsorbent composite according to claim 12 wherein said cationicamino-epichlorohydrin adduct is a cationic polymericamino-epichlorohydrin resin.
 26. The absorbent composite according toclaim 25 wherein said cationic polymeric resin is a reaction productbetween epichlorohydrin and a polyethyleneimine or apolyamide-polyamine.
 27. The absorbent composite according to claim 12wherein said substrate is selected from the group consisting of fibrouslayers and foam layers.
 28. The absorbent composite according to claim27 wherein said substrate is a solid foam layer having an average poresize of from about 1.0 microns to about 1000 microns.
 29. The absorbentcomposite according to claim 28 wherein said solid foam layer has anaverage pore size of from about 1.0 microns to about 200 microns. 30.The absorbent composite according to claim 29 wherein said average poresize is of from about 5.0 microns to about 70 microns.
 31. The absorbentcomposite according to claim 30 wherein said solid foam layer is a wetexpansible foam layer.
 32. An absorbent article comprising: (i) a liquidpervious topsheet; (ii) a liquid impervious backsheet; and (iii) anabsorbent core positioned between said topsheet and said backsheet,wherein said absorbent core comprises at least one absorbent compositeof claim 7, 8, 9 and
 10. 33. The absorbent article of claim 32 whereinsaid absorbent core further comprises an acquisition componentpositioned between said topsheet and said absorbent composite.
 34. Theabsorbent article of claim 33 wherein said acquisition componentcomprises a member selected from the group consisting of chemicallystiffened cellulosic fibers, air felt fibers, synthetic fibers,hydrophilic absorbent foam materials, and mixtures thereof.
 35. Theabsorbent article according to claim 10 wherein said absorbent articleis a diaper or an adult incontinence product.
 36. The absorbentcomposite according to claim 10 wherein said particles are made from apolymer material selected from the group consisting of hydrolyzedstarch-acrylonitrile graft copolymers; partially neutralizedstarch-acrylonitrile graft copolymers; starch-acrylic acid graftcopolymers, partially neutralized starch-acrylic acid graft copolymers;saponified vinyl acetate-acrylic ester copolymers; hydrolyzedacrylonitrile copolymers; hydrolyzed acrylamide copolymers; slightlynetwork crosslinked products of any of the foregoing copolymers;partially neutralized polyacrylic acid; slightly network crosslinkedproducts of partially neutralized polyacrylic acid; and mixturesthereof.
 37. The absorbent composite according to claim 10 wherein saidmacrostructure is a sheet having a thickness of at least about 0.2 mmand a density of from about 0.6 to about 1.1 g/cc.